I've been thinking about running some tests on this but haven't really had time. I landed an Inner Beast on a boss, was almost dead, and got 2013 HP back (highest so far I think) I'm usually not really watching the #'s when I swing though, and I don't run a parser.

I usually hit Berserk, Blood Bath, Convalescence, then SC Storm's Eye, and THEN pop IB. Typically get's me ~1K HP from bosses. I try and use my cooldowns so I can do 2 at a time, while at low health. Circling back to your post, sometimes, without noticing the exact #'s, It looks like I don't get healed as much, and I think my 2013 was indeed after a Butcher's Block.