Hi Roland,
I have an IO-360-A3B6D (i.e. heavy) and I set my cowl about 3/16" low, and after about 40 hours it appears to be perfectly aligned (no acro, though). That being said, I didn't even notice that the cowl was set low for the first bunch of hours so how much (or even if) you set it low may be debatable.
Cheers