Purpzie
It took me forever to figure this out. For some reason, advanced contact parameters (or at least sender local position, from testing) can't be used to drive AAPs. It's incredibly weird because contacts normally allow you to do that.
(AAPs: https://vrc.school/docs/Other/AAPs/)
This behavior is needed so we can apply scaling using a blendtree to multiply by ScaleFactorInverse, remap values, among lots of other uses.
Here's an avatar that detects your head rotation using sender local position. Each animation moves the cube behind you and drives a
HeadAngle/
AAP. The cube moves, but those AAPs don't change. You can check in the avatar debugger. https://vrchat.com/home/avatar/avtr_ec965727-67de-45b9-9476-411a27849ed2
I wonder if this has to do with the timing of contact updates...