Originally Posted by Overlord Rion
That attack roll was the concentration check, I just didn't label it as such since it replaces the attack roll.
As for the miss chance...
From how I understand it, you roll a Concentration check against the target's AC, and if that succeeds, then you make an attack roll against their flat-footed AC. If you fail the Concentration check, you still make an attack roll, but at a -2 penalty and no bonus damage dice.