I think it's a bit premature, but I'll add that to give you something to play with... my concern is that you'll fixate on doing the Capsule mapping or something - which gave decent results in your earlier test (especially with closely aligned meshes, where the ray doesn't travel far), but will fall flat (as it were) for things like the top of the nostrils - the ray needs to head in a generally downward direction to hit the top of the nostril, but it's Cylindrical path (in that zone) will cause it to head sideways, instead (for example).

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