Hi there - I have solved this for you. I have the sidereal calculations working for both ascensional times and Ptolemaic primaries. The solution in both cases is to re-apply the value of the ayanamsa to the longitudes. So for the primaries, I have had to add the ayanamsa to the longitude of the sidereal MC, effectively reversing the sidereal 'correction', so that the RAMC is the one that would have been used with the tropical MC. Then the ayanamsa needs to re-applied to the longitude of the ascendant and each bound cusp. This also effectively reverses the sidereal 'correction' for the movement of the ecliptic across the horizon to give the tropical oblique ascensions.
So, in conclusion, the rising of the sidereal bounds can only be calculated by hybridising the sidereal values and the tropical values. I have to be honest, this sounds like a mash up to me, and quite bizarre. Are we doing sidereal astrology or not? It seems to me that in this case we're not, but just overlaying the sidereal zodiac onto something that, at its foundation, is tropical. This really throws the whole sidereal zodiac into doubt in my mind. The fundamental issue is the uncoupling of the right ascension of the MC from the oblique ascension of the ascendant when using the sidereal zodiac. My view is that this technique - ascensions through the bounds - can only be deployed by effectively reversing the sidereal correction, calculating tropically, and then working 'as if' the sidereal zodiac is still in use. I find it difficult to know what sense this makes.
Another way of looking at this is that degree of the sidereal MC is not the degree of the midheaven crossing the meridian at the time for which the chart is drawn. It's difficult to know what the sidereal MC means in this case, if it is uncoupled from the meridian. The sidereal correction removes this link and it is only by restoring it, to return to the original RAMC and the tropical MC, that the technique can be calculated correctly. The issue is similar with the ascendant. The sidereal degree of the ascendant is not associated with the oblique ascension of the zodiac that is actually rising at the time for which the chart is drawn. Again, it is only be restoring the ayanamsa value that the correct oblique ascension can be calculated. I may be missing something, but I'm pretty sure this is what is going on.
I'm sorry to speak so plainly, but you might wish to reflect on this. You are, of course, welcome to draw your own conclusions. Valens might have been using a sidereal zodiac, but with the modest ayanamsa correction made in his time, and the levels of precision he was concerned with, I don't think it mattered. But clearly, with an ayanamsa of around 22 degrees, it's quite a different matter.
I will test this some more. Once I am assured that it is working OK you are welcome to have a bespoke copy, but I'm quite unsure whether to release it generally.
Thanks for raising this most thought provoking scenario. It's been helpful to work through.