Space above the rings? Are you referring to the piston to cylinder wall clearance just above the top ring or does what you're saying have something to do with the deck height of the block (My motor from the factory had a zero deck height as does the combo I have now)
That's very interesting indeed...
I've never computed a CR by cc'n the head with the gasket and all that, that's Smoky Yunick stuff there!
So when ordering a set of custom pistons from say, JE, and they ask me what the cc on my heads are, when I tell them I would like a set of 10.5-1 slugs are they factoring in all of the tolerances you've mentioned?