The thing is, it's already a feat that people are going to complain about (Fast Healing is generally perceived as much stronger than it is, past the first point), and the difference at high levels between Fast Healing 2 and Fast Healing 5 is actually almost completely nonexistant (3HP/round). And, as mentioned, it's a modified version of an existing feat from Bloodforge, Overflowing Life, and I'd rather not just make a stronger version of it.