if I read you correctly re the knife edge, you bed underneath there, out to the edge, but the knife should be just above the bedding.
this is what gives a bigger bedding surface to the rear tang.
not having a vertical surface is actually an advantage.
any vertical surfaces in this area should have clearance to protect the stock.really the only vertical surface in contact with bedding should be the rear of the recoil lug.
front,sides and front of the recoil lug should have clearance.
tape is your friend when using epoxy.
use it anywhere you need clearance.
whatever you do, no vertical surface in the tang area should contact, epoxy or no.
the thickness of epoxy used will not stop splitting.
bruce.