WAR skill Inner Beast

[Agmundr]

Hey all, I've noticed some inconsistency with Inner Beast. At times, it gives what looks like the 300% self-heal (didn't do actual math, it just looks like around 3x as much at a glance), and yet sometimes it heals for less than the damage actually was. I actually had it heal me for 1 whole damage once last night.

I experimented a little with it, and for some reason it seemed to give less when following Maim and more when following Butcher's Block combo. Does anyone know what's up with this? I thought it was supposed to always be 300% self-heal, and I'd like to know how to keep it as high as possible if it's "Up to 300%" (which it doesn't say in the description).