I like pumping with a ring on because my cock stays very near its pumped size after coming out of the tube. But, as you say, it's really tricky to find a cylinder, bottom seal, and ring size that will keep the ring at the base of my cock but not inside the tube! Because I'm also thick at the base (girth just under 6.5"), I use a 2.5" diameter tube and modify its bottom seal (it's inner diameter is far too small to let me in) and use a metal ring that's snug around my cock but just a bit too large to fit inside the tube. Because I stay at nearly in-cylinder size for an extended time, it does seem it would do a better job of permanently enlarging the cavernosa tissues ... and it just feels and looks so great to be that big for so long! I love edging in that state ...