Yes, you need to modify animation blueprint in the “Update Fingers from SteamVR” collapsed graph: https://pp.userapi.com/c848524/v8485…4MPQV5siQ4.jpg
By default, I only use curl values. Also, keep in mind that you probably need to use some multipliers (may be negative) for splay values.
Also you can modify reference pose (pose for open hand; rotation of fingers is calculated relative to this pose).
