Stretched length vs erect length and other things

I am feeling kind of discouraged and at a crossroads. I want to describe what I have been doing, and see if somebody might offer advice.

Mostly I want to gain length. I started haphazardly and inconsistently jelqing with my hand and later a tool a few years ago. I probably gained an inch in length and girth, but I have not kept good measurements and records. I suspect those gains were the newbie gains people talk about.

I have a pump, but for the last couple of months I have been using the LeLuv slider extender. I have read that extenders are better for length gains.

Anyway, I can’t do the 4-8 hours recommended. I don’t know how anybody can do that actually. Instead I have been using the extender to stretch as much as possible and hold that stretch for about 15-20 minutes. After 15 minutes or so a stinging pain begins where the base of the extender digs into the scrotum. I remove the extender and wait at least 10 minutes before repeating. At most, I might do 8 stretch sessions of 15-20 minutes each (2 hours total). Some days I only do a couple of stretch sessions or none at all.

Getting to the point (sorry for rambling). I think the maximum stretched length has increased almost 1/2 inch, but I don’t think the erect length has increased visibly. I am measuring the stretched length using the penis pump, because I think that is a consistent way to measure.

Shouldn’t the stretched length affect the erect length?

Is my method of using the extender a waste of time?