logic is overrated
Sex is more fun than logic. One cannot prove this. It simply IS, as Mount Everest IS.
It's also possible to get off without being hard. It's not easy, but possible.
I found out today that I could definitely potentially do this, I can bend myself nearly an inch past my tailhole, so long as I'm just starting to get excited. It would be really tough, though, since I get a large amount of growth during arousal.
As far as sucking oneself, I can't even touch the tip. I also have a lot of problems maintaining arousal when trying this, so that doesn't help.