Here's some info. I just did a quick test of the TSX ASCOM driver. I used POTH to see what functions are being used. When the "inhibit sync to protect model" box is unchecked, POTH shows that CanSync is true (a check mark). When inhibit sync is enable/checked, CanSync changes to false (unchecked in POTH). And that's where the problem arises, centering never converges without the sync. So if I understand you correctly, you are not sending a sync command in that instance anyway and therefore the parts of the discussion referring to centering with or without a sync are somewhat moot.
So at baseline, ASCOM driver for TSX is functioning as you expect, and it works fine. The change in functionality is one that SB made and seems to be in TSX itself and changes CanSync to false regardless of the ASCOM driver setting. And unfortunately, TSX must be running for a Paramount to function.
So I think a better direction for the discussion is can SGP's centering be made to converge as expected without the sync command, because you aren't sending it anyway if CanSync is false? In the meantime, I'll just continue to use TSX 10.3.0 which works fine with SGP. 
Thanks for your time and consideration,
Chris