Pigeon pose is meant to stretch the piriformis muscle. The intensity of the stretch in pigeon pose is determined by the alignment of the back thigh, and the front shin in relation to the hip and the front of the mat or pelvis. The closer the shin comes towards parallel the more powerfully the piriformis muscle stretches.
If pigeon pose is daunting for a student and it often is, I will suggest the they elevate the pelvis to make it easier to get centered on the back thigh. Something I never do is to suggest that students put a blanket under the hip of the front leg. It seems counter to the point of pigeon pose. The logic is that the blanket will allow the pelvis to be level but instead I find that students tend to roll away from the correct alignment of the back leg onto the blanket. From my perspective, all this does is take some of the power out of a stretch that is meant to be fierce.
Everyone goes to yoga for different reasons. I go because I have some muscles that work better than others and I am trying to bring all of my muscle groups into balance. To that end, I am looking to stress my body out to bring specific change. Pigeon pose is a perfect example of this. If your piriformis is tight it won’t change if the pose is easy or misaligned. If you let the weight of the front hip release onto a blanket you are most likely making the pose easier. The effort involved in having a level pelvis without a blanket is part of the work of the pose.
When you align the body so you are directly over the center of the thigh of the back leg, you will hit that sweet spot in pigeon pose that doesn’t feel all that sweet but is where you want to go.
The key to aligning the pose correctly lies in the back thigh. However high you have to lift the hips to roll directly over the center of the thigh is the proper position of the pelvis and the best alignment of pigeon pose.
The piriformis is one of more profound muscles in the body and one that is often deeply in need of stretching. You might as well go for it and stretch it as much as you can.