I never really knew any technical numbers on this subject. Just hillbilly style engineering that made sense to me...lol.
With stock style closed chambers, I used to lay back the intake wall a little bit.....especially on overbored engines. I used the scribe method to make sure I was close to the actual bore size. How well it worked? Beats me, but i figured it couldn't hurt. I never used oversized valves big enough to get near a interference point between them, so I'm clueless there.
A example below of what looks like a pretty shrouded chamber is the "true" closed BBC. Looks a little ugly as far as what we're talking about here, but maybe looks are deceiving. Although they did lay back the plug side of the chambers on performance spec'd engines...
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I guess the 348/409 engines below were the true idea of un-shrouding. Even though the chamber was in the cylinder and was formed mainly by angle mounting and the piston dome, the fact that the piston was away from the deck for most of the event had to alleviate any issue with shrouding i would think. Maybe on the intake cylinder wall side if a large valve was used? Although they were very large bore engines.
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I'm sorry I used Chebbies as a example, but since the discussion was in general terms, these were the best examples I could find.