If you have been following my work, you may have read the book that the title of this thread refers to, in which I mention my objections to the term 'western astrology'. In my opinion there is no western tradition of astrology, in any meaningful sense, until the early modern period. The astrology that I do would have seemed quite familiar to a medieval Persian astrologer, but that style in itself contains elements derived both from India and directly from the Hellenistic world. There are no 'pure' astrological lineages, nor any real east/west divide; rather, as Pingree said, the transmission of astrology progressed 'in appropriate circles'.
In my opinion, the ayanāṃśa question can't be divorced from the overall calculation of planetary longitudes, where we all (presumably) use modern values rather than, say, the
Perpetual Tables or a medieval
zīj. I vaguely recalled an old but interesting paper by Therese Hamilton where she found modern recalculation of longitudes with the Krishnamurti ayanāṃśa often to be the best match for longitudes given in Babylonian tablets, and after some searching I found it
here. If memory serves, I have also seen a similar comparison (by Therese or someone else) based on early Arabic-language charts, perhaps from Māshāʾallāh. Sorry to be so vague, but this is just from memory; perhaps someone else knows what I mean and can give the reference.
I don't think there is a value in adhering to ancient (or medieval) astronomical/mathematical models as such. Doing so could land us in some very odd positions (trepidation, anyone?). For instance, Vettius Valens explicitly supports the Babylonian definition of 0° Aries as located 8° prior to the equinox, which he clearly regards as a fixed value. This is neither Ptolemy's tropical zodiac nor a sidereal definition in the modern sense, because Valens didn't understand precession. But I'm not aware of any modern Hellenistic-style astrologers actually using Valens' preferred zodiac when applying his techniques.