Penis grows about 1 inch depending on how i masturbate??

I remember that when i was still with my last girlfriend and used to have sex, i used to see my penis bigger, i thought it was just an optical ilusion since i was sort of half sitting half laying down a bit and saw it closer, maybe it was just a little bit bigger since i was actually having sex, for context it was almost always exclusively her on top since that's what she liked most.

Uhhh so today i discovered none of those were true, turns out that if i masturbate with my penis facing up instead of forward like i always did, it grows a about whole inch give or take.

I suppose this has to do with blood flow obviously, but why upwards? I would understand it more if it was whilst facing down, since it makes sense blood would flow better that way, i mean whenever my arms for example are facing down for a long time they start getting more veins visible on them that when they're facing up.

And by this much? This takes me from 6,5 inches, about average to 7,5~ inches, which i would start to consider big.

It's even noticeable without comparing, normally i masturbate in the toilet since it's cleaner, and about once or twice a month since i have a pretty low libido, always had it.
But anyway once it grows it doesn't even fit inside the bowl, and my back is fully pressed against the back of the toilet. It also becomes girthier, about a bit more than 3 fingers wide, but only at the tip and a bit of the upper shaft, giving it this mushroom shape.

And i'm making this post because i'm genuinely concerned, i haven't seen this happen to anyone else, at least not by this much.

Is my blood flow bad? Should my penis be bigger when masturbating normally? Some other kind of medical issue? Should i tell this to my doctor next time i see him?

For a bit of context not too long ago i had iron-deficiency anemia and i'm pretty skinny.

Help appreciated!