Only healing when entering blood would nerf leech to completely useless status.
Why would you waste AP moving your character to blood puddles, subjecting them to Opportunist attacks or environmental hazards, when you could just use cure wounds/water heals/healing pots? I agree leech is too strong and trivializes physical damage greatly, but some of the initial healing needs to be retained or people would stop using it.
Also, I have found it to be much stronger in earlier levels than later when enemies hit much harder.
