combustion chamber question

Combustion chamber size plays a role too; the larger it is, the longer to conbustion process takes, and the more chance to detonate. So closed chambers help in that regard.

As a point of info, a local Ford machinist who builds a gob of 2.3L 4 bangers told me that they have built quench gaps pretty short but at around .025" gap + or -, the pistons juuust start to kiss the heads in race conditions (hot, high revs). This is for circle track racing. So I generally take that a an absolute lower bound on what you might do, but the .035 lower limit is a practical street build limit.

IMHO, the OP is skirting detonation problems with flat tops if things are not just right, if his math is right and SCR is 11.5. AJ's DCR number is pointing there too. For general street use, and the lower max octane fuel in Oregon, I would not go there personally.