Many expert pumpers have gained length from pumping along.
I think it has to do more with the size of the cylinder. A guy with 5” girth and uses 2” cylinder may likely to gain more girth than length. If he uses a tighter fit cylinder (1 3/4” tube), then his penis is likely to expand upward during pumping because there’s little room to growth width wise.
I am about 5” base girth and I use 1 3/4” cylinder. When I add pressure during pumping, my unit expands upward but very little width-wise. I purposely get a tighter fit cylinder because I want to gain length (and some girth).
Notorious "Hardgainer". No Gain in 4 Years! Check out my "Blog" under Profile.
(starting: Jun 2007) 5.75" BPEL x 5" EG / (Sept 11, 2011) 6.375" BPEL x 5.125" EG / (July 1st, 2014) 6.25" BPEL x 5.125" EG (lost a bit of size)