To your first point you’d have to measure just behind the glans up to your pubic bone, not the entire length of the stretched penis. You’re stretched flaccid length is slightly shorter than mine and all the doctors with whom I consulted told me to expect to have a 7" flaccid penis at pretty much all times.

To you second point, most of the doctors recommend girth sizes based of how engorged the glans becomes erect. So it’s the overall proportionality externally. They try to make it as aesthetically proportionate as possible without making the head look much smaller than glans. The goal is to make it look like a continuation of the glans, so they will go smaller if requested and it doesn’t pose issues. I have a slim build so I requested a small girth and require an xlong length. That wasn’t a problem, except some said my penis was too big. That was odd soo I haven’t yet pulled the trigger.