I just had my +2 hellbent commander amulet go to +5 total. It's on 10/12 and it hit the crit on 1 and 2.

So that would mean:
8x 5% = 40%
2x 25% = 50%

So a multiplier of 1,9
2 x 1,9 = 3,8

And it's on 5...

Yea my spreadsheet is garbage... idk wtf blizzard is doing. The only way it gets to 5 is compounding increases. Do you know if it went to 5 at precisely 10/12? Seems like you might get to 6 if it rolls again at 12.

I can't remember, I think it did hit it on 10/12 yes. Can't roll a 3rd time anymore, as I have it on 12/12 now and not going to reset it

If you can get a +2 skill up to a 6 this game is broken

My +3 Golem Mastery chest went up to +4 Golem Mastery with only six 5% increases (not really sure how that worked).

That actually makes sense. Everything in my own game I've checked has been additive, justbart's weird situation doesn't make sense. You get .15 skills per 5% increase so 6 increases is .9 skills. It seems like passing .5 skills is what bumps it up, unless you're saying it didn't level up until the 6th then we're still not sure where the threshold is.