It looks like you're using a little too much base timing. My own combination never runs more than 32deg total on the top end. I see yours around 37. I don't run that much timing even on E85. That's more for light cruise and trailing throttle.
I second this. If you set the IAM to 1 (100% coarse spark advance or all of your learned spark) and you get knock as you describe, you are running too much base spark advance. take 5 degrees out of your base map in the areas where the knock is detected, then try again.
3-4% of 15.3 ms doesn't seem like a meaningful amount to me. I would ignore it.
1) Keep IAM at 1
2) reduce base spark advance in areas where you got knock
3) keep logging
4) not get hung up on fine spark advance