Issue using mutiple poses in a Pose Asset for facial animation

I’m looking into sharing facial animation between characters with the same skeleton and morph targets and been following this approach seen in the documentation:

So far I’ve managed to set up two characters with the same skeleton, morph targets, Pose Assets, and a curve animation to drive them with. The Pose Asset is driven by the anim curves just fine but it doesn’t appear correct due to how it sets the values to the anim curves.

The issue appears to be when two poses are set to 1.0 in the Pose Asset, the resulting anim curves are set to 0.5 instead. It seems that it’s trying to set all anim curves at once instead of adding them together which is what I’m looking for.

Does anyone know what might be causing this issue? This is the only issue preventing me from using this approach and I’m out of ideas.

You have to enable “additive option” in “asset detail” of “pose asset”.