Reverse transfer, at least the type that i am suggesting, isnt the same thing as muat life-drain.

Drain does damage first, with the secondary effect healing the drainer for some ratio of the amount of damage done. If the drainer isnt hurt at all, they can still do damage (i believe, havent actually played a muat).

Reverse transfer would only deal an amount of damage up to the amount of health the user was down, so a fully healed psion would not be able to transfer any damage to anyone.

This is similar to the way that a psycian can only drain psi up to the amount they are down. If they are full, they cannot drain anything.