RE: Where should i place the cross hairs?
If you are aiming in the center of the rib cage, then you are gut shooting the deer.
You also said you are aiming left of the leg, (depending which way the deer is facing)to shoot it in the lungs, you should put the cross hairs just behind the the shoulder 1/3 to 1/2 up the body and no more than 1/3 back from the front of the deer.