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.
It would heal you the first time you get hit (since you have 'entered' a pool of blood). It would then STOP healing you, until you exit that pool and enter a new one. Imho Leech should not be a complete game-changer. It should be a nice bonus that usually helps you a little. I think that would put it in line with most of the other talents.
