This has been my experience and using a common sense approach along with simple logic it dawned on me that as my veins became visibly larger my penis was getting considerably larger. This increased size is primarily girth related but it also translates to length.
I do not know if anyone has experienced isolated incidences of a significantly larger erection (length) due to altitutde changes or physical workouts, but I would have these experiences (quite rare), one time in Aspen during spring break I was with my gal and had an erection like I had never seen before (it was at least an inch longer than ever before - this is pre-PE). This is all attributable to the blood flow characteristics being affected. Anyone successful with a PE routine (with at least a year invested) will have visible veins and arteries that are 2 to 4 times there pre-PE capacity (diameter).
And to think some gals hate a veiny penis, I guess when it’s buried deep they let out a different scream.