Imagine having hips so wide that you can shunt someone else's entire head up your ass, nestling it snugly within your hips entirely and it not even making a bulge. Their head entirely concealed between your pelvic region and your abdomen still acts like there's nothing in you. I bet anyone is a comfy chair at that point, resting upon their shoulders, just better hope they don't tuck their shoulders in or else your belly might start showing signs of filling... and maybe you'll be sitting flat on the floor with a new dildo instead of a chair~