Girth PE seems to increase erection quality for me, with the exception of flaccid pumping.
The nature of the erection is that the inner girthwise fascia must be able to expand to compress veins against the outer lengthwise fascia. If the inner fascia sheath is enlarged and more flexible, the erections should be harder on a solely mechanical basis. Basically, the penis structure creates a mechanism where by the force of the blood flow into the penis reduces blood flow out of the penis. But all that hinges on the ability for the inner fascia to expand enough under the increased blood flow during arousal.
My thoughts are that flaccid pumping does not necessarily exert force equally within the penis. The outer fascia can be pulled into an enlarged state by the pump, while fluid gradually builds up between the inner and outer fascia. If you have a hard erection in the tube continuously, the inner fascia keeps that space under pressure so fluid cannot fill it and the inner fascia expansion keeps up with the outer fascia expansion. I haven’t tried aspirating the space though. I bet you could see it with an ultrasound imager though.
Starting: 7"bplx5.2" 2017 (shrunk from disuse)(originally 8"bplx4.5", gained to 9"bplx6")
Current: 9.0"bplx6.125" 2020
Goal: 11.5"bplx7" 2021.