A picture of how far the piston skirt comes out of the hole on bottom dead center would be interesting. If there is much it might explain why there is some blowby into the catch can. Maybe some piston rock at BDC is unseating the rings under boost. It could just be a light oil ring pack too. A fish scale pull with just the oil ring on the piston might give some useful info. When I was building motors I found that the lighter ring tensions would show power but at the expense of an increase of blow by. Some times we just added a vacuum pump and picked up power. And sometimes we just vented it out the crankcase into a catch tank. Either way is would be something to look at. This is interesting.