Metahuman Rig Using 100% Blendshapes

Hey Guy, I have a question about how the metahuman rig is achieving each of it’s poses and adding each pose together when activating multiple controls. I’m using a 100% blendshape rig which are matching the poses made by metahumans 150+ expressions, the trouble I’m having is when certain shapes are combined together I seem to get a different result than the metahuman rig, is there some kind of interpolation between some poses or some in between poses when two controls are active together, or are all poses additive when activating multiple controls?