Could it be possible that the Cobb AP tune has cylinder 6 running a bit richer due to it being a hotter cylinder? I know in my S2000, we have a bit more e85 going to cylinder 4 because it's the one that gets the hottest. Even though full boost AF in the S is targeted around 11.8 on my WB o2 for all 4 cylinders, cylinder 4 is still getting a bit more fuel than the other 3 due to the way my tuner set it up.
11 E92 ZCP
02 Honda S2000
-741 whp 471 wtq (dynojet) @ 29.6 psi on e85; now on 34 psi, 800+ whp.