...= 19.63
Let’s say that the tunes were matched somehow in the two different bores and everything else remained unchanged:
1,000 lbs/si * 19.63 si = 19,630 lbs force
1,000 lbs/si * 12.56 si = 12,560 lbs force
This is still a 36% increase in force on the piston:
(19,630-12,560)/19,630 = 0.36...