Big Swede…you do not have to have a large cock head to successfully fit the strap over the head to hold it tight. It won’t slip out. It straps behind the head. The device can move around with you as you move. They recommend it hand downward.
I have mine set with enough tension (Pull) for a moderate stretch. You can set it my adjusting the pull to what you want. I don’t pull real hard when i do manual stretches anymore. I think a moderate pull is best for me. You may want to consider other cheaper devices, they may work just as well. Also, consider none of them may work I guess. Time will tell if this helps in growth or not.