340 High Compression Pistons

Even that piston calls out to be out of the deck .018 and that probably isn't enough. I'm at a skosh over 11:1 with a small dome and I'm .045 out of the hole. I did leave my heads at 68cc's because if I took much more off I'd start hurting flow.
Curious..... what head, and what is the mechanism in your case to hurt flow?