Sorry, folks-- I'm a latecomer to this thread, and am now only part way through. If I don't jump in when the spirit moves me, I'm apt to lose my points by the time I've done all the homework.
First, thanks Paul for taking this discussion here. I deliberately avoid social media out of privacy concerns, so it's gook to rekindle hot topics on the Skyscript forum.
A very tiny fly in the ointment-- Hellenistic or ancient astrology was not necessarily typified or defined by the "literary sources." Not only do we know that an awful lot of material was lost or preserved in part through secondary referencing, but historical sources of the Roman empire indicate practices that aren't event mentioned in the translated written sources.
One such practice was the use of astrology boards. We don't precisely know how they were used. If memory serves, they weren't mentioned in the published sources (that I've read.) For example, :
https://www.livescience.com/17943-oldes ... odiac.html
It looks to me like whole signs houses would be the easiest houses system to use with these boards. Which isn't to say that some other system could have been applied, but with more difficulty.
We know from the extant published sources plus Frederick Cramer,
Astrology in Roman Law and Politicsthat all kinds of people practiced astrology: slaves, women (gasp, shock!) and people at street fairs. The "good" astrologers complained about the charlatans, but the fact remains that some people were practicing astrology in Roman times that differed fromn the kind sanctioned by Ptolemy or
Firmicus Maternus. Not to mention Mithraism and the use of astrology in Hermeticism and Egyptian black magic. Probably a lot of these alternative astrologers didn't use houses.
Then we have a collection of a lot of archaeological finds of verbal horoscopes in Neugebauer and Van Hoesen's monograph on Greek horoscopes. Some of these came with degrees, but many were just planets-in-signs.
I once worked out all of the Valens horoscopes that had sufficient data for that purpose. The only way I could get them to work out was with whole signs. Clearly Valens knew about additional house systems, but I don't know how much he used them himself. Valens was a great compiler of other people's work.
Dismissing Manilius as a poet seems to me to be taking him out of all historical context. We don't know whether he read charts for people or not. He continued an ancient tradition of believing that poetry, not prose, was the proper medium for writing about the heavens and the gods.
Anubio (1st century CE) also wrote in poetry. (Stephan Heilen, "Anubio Reconsidered.")
I agree with Houlding, Ross and Greenbaum
https://www.academia.edu/7370462/The_Ro ... _Horoscope
that the origin of houses was probably Egyptian-- and steeped in ancient religious beliefs. The Egyptians' minute observations of the heavens with their decans system and the all-important rising of the sun probably gave rise to the ascendant or "horoscope point" in astrology.
They used a system of natural hours, in dividing day and night into two separate periods of equal length. I believe that the planetary joys in houses-- however much they were subjequently rationalized by the Hellenists-- were based upon the stations of the sun/pharaoh/soul passing through the night/afterlife at night; and then the stations of the sun during the day.