For side sleepers like me, the Bi-Pod Bivy is way too tight in both the hip and shoulder areas. Also, I use the Thermarest Neo-Air mattress which when fully inflated takes-up three inches in height.
I have reordered and have received the heavier but far more spacious Tri-Pod Bivy. Its size is just right for me.
The quality of both models is excellent.
I have two complaints with both models. First, the zip-up opening is much too small. The opening should have at least one more foot to facilitate entry into the bivy. Second, I dont understand why the outer seams dont come pre-sealed from the factory. Instead you are sent a tube of sealer and a syringe and must do it yourself.