I have been trying to find some exercise that will isolate the CS(the underside of the penis). Is it supposed to be "spongey" even with an erection? I've seen guys in adult entertainment and pics of other guys whos "underside" looks nice and full, while mine remains soft and spongy. It's very annoying for me, and I have a compulsion that I really want to fix it. When I'm erect, the CC feels fine, but the CS just feels like it doesn't have any blood filling it.