The map plays fine even with HP7 (just testplayed it, even missed some of the 1/8s on purpose and didn't fail). I also played with HR (HP7) with misses and didn't fail. It's a fact that the hp bar is not full, but this means nothing. If you play the map bad then you fail, that's how it works. HP Drain no less than 6 would be appropriate here, though 7 works too but it's your pick.