Explain references in pose asset

I started to use Pose Assets for facial animations and I’m really having a hard time getting this right. My particular problem is that I have a unified skeleton for male and females using different meshes. The imported facial anims and poses together with the blend nodes sometimes produce grotesque abominations.
I found out through a lot of trial and errors that it has to do with
Setting or not setting additive in the animation
Setting or not setting additive in the pose asset
chosing the right reference in pose asset
clicking the Update Source button when you make any changes (took me 6 hours to hit it by chance)
chosing the right Retarget Source in the drop down in pose asset

I really think there should be a manual page that explains all that in detail. I got mys tuff working, but I have no idea why it works nor what all these double layer “reference poses” are and what they reference. Clarification is necessary