riverhawk

There are three oak trees on my property--a squirrel hotspot--backed right against a tall, rocky hill. I think the hill is thick enough to be an adequate backstop should I shoot squirrels out of the trees, but the question is how should I change my aim if I'm shooting up from the ground? (Not right under the trees, I mean up and forward of course.) I'm using a .17HMR and not doing long range, only out to 80 yards.

Thanks,
Riverhawk