dont forget deck height too. Like the reason the B16B pistons have the highest dome of them all, but in a B16B block only have a 10.8:1 CR. this is because the deck height of the B16B block is the same as the B18C blocks (just destroked with shorter rods), but taller than the B16A. so, the piston does not travel as close to the combustion chamber as they would in a B16A motor.
EDIT:
and something is wrong with that compression calcualtor, because they say the B16B/B16A blocks have the same deck height, and they do not.