Frequent reason why the block's deck height is progressively worse from end to end: it was milled once, but not accurately. Same thing with chambers - size different as you go down the casting.
Quench pretty much stops helping after about .060". The smallest clearance is 1 molecule short of smacking the head when at full temp & RPM, perhaps as small as .032" with tight pistons but using .040" is easier on the nerves and 90% as effective.
