Ugh - this has nothing to do with ascom or sync behavior. The sync is working fine - it just has no benefit at all when there is inherent overshoot hitting a target. That is precisely why I and others see the centering routine stop improving and get stuck at a location slightly away from the object. That error is NOT due to sync or the pointing model or ascom or anything. It indicates that the mount did not land at the ra/dec values it was aiming at. The mount model is fine, ascom is fine, sync is fine.
The mount is also fine - it is just aimed to land VERY CLOSE to the destination ra/dec values - but not perfectly.
For other mounts - sync behaves differently from what sgp expects. And some mounts should not be sync'd at all.
Rather than just blame the mounts - there is a simple and elegant solution that I think would work for everyone - and it could still allow sync if you want it. Simple, elegant - and the result is good performance for everyone at a low price - with no requirement for high end mount behavior.
Frank
[edit] Oh I see you are talking specifically about different sync behavior. Yes I guess that could land in what ascom requires sync to do. But there are good reasons to have it behave differently from what sgp wants - and some mounts allow different settings.
For me sync is ok but there is error in landing - that is repeatable.