Danièle Jay in her last book 'Le Ciel en mouvement' delivers a good understanding from the teachings of the late Giuseppe Bezza.
In chapter VII, she analyses chart examples from the point of view of Ptolemy's Tetrabiblos, Book 4, Chapter 5 on marriages.

Harmony
We know that Ptolemy's view on marriages was rather succint as he considered only the Sun and the Moon for compatibility and the harmonious aspects and reception between the Luminaries (namely the sextile, the trine and signs that 'see' (antiscia, equidistant from the solstices) and 'hear' (commanding - North declination and obeying - South declination, equidistant from the equinoxes with same opposite declination) each other. Ptolemy is not talking about the conjunction.
She cites Valens 'Not only the luminaries but their ruler' (Anthology, II,3)
And later she suggests to add Venus and Mars in the synastry.

Discord
"If the benefics aspect the inharmonious configurations of the Sun and the Moon, the common life does not then seem seriously or definitively threatened. Reconciliations will take place, affection and tenderness will be preserved."
"On the other hand, when the malefic planets look at these same inharmonious configurations, life together will be conflictual, unpleasant, without profit, separation with physical or mental abuse." (p.219)
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For each partner, you look at the Sun and Moon to assess their strength and condition (Luminary In Sect, gender, rulership, Oriental vs Occidental, House placement, aspects, Lunation phase)
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On page 223 and 224, quote "The Lots can also intervene in the destiny of love, as Giuseppe Bezza has clearly shown.
Links exist (between partners) in the following cases:
- Fortuna of one partner with the Sun or Moon of the other partner.
- Fortuna with Daimon
- Daimon with the Moon
- Fortuna with Fortuna
Lesser
- Sun with Sun, ASC or MC (here the connection with the MC can show a partner who will have a say in the career development)
- Moon with Moon, ASC or MC
- ASC with ASC or 7th ('when the Horoscope of one is the 7th sign of the nativity of the other, the days of their union will be long' (Kushyar ibn Labban)
- We can also consider the NN (Jupiter) to increase and SN (Saturn) to decrease.
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On page 210
"A usual horoscope considering only the planets, signs and houses, seems as poor and skeletal next to a chart of Parts as a building which does not yet have windows, doors, or even walls, next to a luxury hotel." (Alexandre Volguine, Cahiers astrologiques, no. 152, June 1971)

The Lots can help personalize a relationship
You can start with the 7 Hermetic Lots and I recommend this link
https://sevenstarsastrology.com/twelve- ... -the-lots/

1 Lot of Fortune (Moon)
2 Lot of Spirit (Sun)
3 Lot of Eros (Venus)
4 Lot of Necessity (Mercury)
5 Lot of Courage (Mars)
6 Lot of Victory (Jupiter)
7 Lot of Nemesis (Saturn)

My personal approach here is fairly simple. Each of these 7 Lots can be viewed as the 'place' of each of the 7 traditional planets and it does provide additional information about the synastry chart.
Let's say you have the Lot of Courage (Mars) conjunct Venus of the other partner, this will be like a Venus/Mars connection, a passionate and dynamic relationship.
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You can investigate other Lots. For example the Part of Sickness conjunct Venus in Virgo (Fall, Out of Sect, Cadent squaring Pluto) in Eleanor Roosevelt's chart reveals her partnership with a partially paralyzed husband.
Looking at a synastry chart, we use the planets positions on the Ecliptic. But do not neglect as Danièle Jay does to look at the charts 'In Mundo', the Right Ascension of the planets measured from the Equator. You will discover unsuspected connections with your partner.

To better illustrate a Synastry chart, let's take the example of Robert and Clara Schumann from Chapter VIII of Danièle Jay, p. 221 (Excerpts from page 221 to 225, Google and free translation)
--------------- Deep agreement between the luminaries of Robert and Clara as well as their rulers.
Clara's Sun conjuncts Robert's Moon, the best possible situation. The conjunction is a bit wide, but acceptable, as it takes place in the same sign, Virgo and the moiety of the luminaries. Each of the luminaries has Mercury as lord, that of Clara sextile that of Robert. The beautiful understanding of the luminaries and their rulers testifies of a deep and lasting loving complicity, similar to that which can bring together two friends brought together by the community of their views and by the pleasure of their presence.
Affection and love are all the greater as the Moon and Venus make mutual aspects with reception.
The difficulties that seem to be looming for the couple cannot call into question a very powerful union, signified by Sun and Moon, by Venus and Moon, while the conjunction of Clara's Mars with Venus and Robert's VII reinforces the physical attraction to each other.

One can also consider the Nodes, North node of Jupiterian essence which amplifies all that it touches, South node of Saturnian essence which diminishes all that it contacts. What strikes here in the 2 charts, it is the superposition of the axis of the nodes, unfortunately opposite, which binds very powerfully the 2 artists. Thus, an element of dissolution, the North node of one amplifies the deleterious action of the South node of the other, while the South node of one lessens and alters the beneficial effects of the North node of the other. It is indeed the dreadful drama that occurred in their life together, the deep love that bound them being corrupted by Robert's illness, by the psychiatric asylum that awaited the composer, and by the separation of death.
(Note: The bindings of the Nodal axis is stronger as Mars/Venus rulers of the Nodes are also tied in their charts. Mars of Clara conjunct Venus of Robert on the cusp of their 1/7 axis. And Mars of Robert square Venus of Clara.
Part of Sickness of Robert 14 Can 29 (15 Can 43 in Mundo) conjunct the ASC/MO of Clara.)

When at the time of the meeting or the marriage, it is normally signified by a primary direction from the Moon to Jupiter, or from the Moon to Venus, secondarily from Venus to Jupiter, finally from Jupiter to the part of the marriage (commentary by G. Bezza in the chapter of the unions Clara's marriage took place on September 12, 1840, when Jupiter in mundo reached the trine of Daimon of Robert (June 29, 1940), and Fortuna joined the trine of the Moon of Clara (July 5 1940).

Post-reading:
In the preface of this book, Francois Saison says: "The principles in her book are simple: day, night, the essential notions of the local sphere, the phases of the planets with respect to the Sun, their hourly distance from the meridian of the place... from birth to the death."
"In the work she offers us today with her usual rigor and clarity, she presents each of these aspects through a dozen examples, in taking advantage of her great qualities as a pedagogue."

After reading her book, I wondered if I ever understood the meaning of certain passages of the Tetrabiblos. At least the way she applies it to the chart examples. A great astrologer to discover.