Blendspace settings questions

I’ve been trying to figure out how to play a one-off blendspace, played above the waist, for a while now. I think part of my problem is I apparently just don’t understand some of the options relating to blendspaces.

Could someone give me a quick explanation of what the sample interpolation settings, specifically the per bone blend, do? The way they’re set up, I thought it would work like a blend node but don’t find it functioning that way. Also, the additive settings on the individual animations making up the blendspace?