Do you generally have your legs more straight, or curled up? I've managed to sleep just fine on my side in every hammock I've tried so far, but I generally have my legs puled up in a semi-fetal kind of position. I don't have any experience with the Black Bird. . . the foot box may allow you to sleep on your side with legs straight without any problems, but I'd think that with most other hammocks you'd be able to avoid the pain by using a pillow or a pad for a bit of support.
Don't alter my altar
don't desecrate my shrine
My church is the water
and my home is underneath the shady pines
From the song "One Man's Shame" by William Elliot Whitmore