It's actually:KISS
shooting low , aim high
shooting High, aim low
Was squirrel hunting, 20 foot away from truck, squirel was about 18 foot high, aimed @ middle of head, hit the shoulder,
Shooting low, aim low.
Shooting high, aim low.
It's the same adjustment whether aiming upwards or downwards.
Hitting lower on the squirrel than expected in the scenario described, is probably due to shooting at very close range.
When shooting a rifle (especially a scoped rifle) at close range, the bullet will hit lower than expected because the bore is quite a bit below the sights. Shooting upwards will make the bullet impact higher than it otherwise would, but probably not enough to get it up to the sightline within 6-7 yards from the muzzle.