Blending two facial metahuman animations in Sequencer while overriding a part

I’m trying to combine two facial animations in Unreal 5.6.
One is a head-only animation recorded internally with AR Live Link; the other is a MetaHuman performance generated from audio (I also have a baked version of it).

When I blend the two animations in Sequencer by setting both weights to 0.5, they do mix, but the head animation I recorded—where the mouth is closed—interferes with and partially overrides the mouth animation from the performance, which I need to remain clean.

Is there a way in Sequencer, or elsewhere, to keep the mouth animation from the performance while using only the head motion from the AR Live Link recording, and merge them together?

Thank you in advance

T