When you cross your ankle over the knee, the bend that is created from the knee will point which way you are going to lean.
If crossing your ankle over your leg is too hard, then just bend the knee and keep the foot on the ground.
Make sure that you roll quite high onto the glute and tilt side to side to massage the entire Piriformis muscle.
Lie on your forearms, try to relax your quads and roll slowly towards the top of your knees. Sit and relax on a spot if it is painful.