Alex, do you do many reverse kegels? Try pushing your erection towards the floor, and doing long reverse kegels.
As I see it, a kegel cuts of blood outflow, so normal inflow can build up to expand tissues. However, with a normal kegel, blood supply vessels aren’t stressed or affected.
A reverse kege has the exact opposite effect, forcing more than normal blood flow through the supply vessels, making them expand to accomodate the added volume.
Perhaps over time reverse kegeling while pushing your erection downwards will increase the size of your supply vessels and alleviate the blood flow problem?
I don’t know how well versed you are with reverse kegels, but try to concentrate on getting the pushing out feeling to center between trying hard to crap or pee. When you get it right, you can really feel the blood flowing in the shaft and head… If this works for you, once your head swells up, trap the blood in the shaft and do uli’s, to expand your glans size, although those cock ring pics show you have good glans potential if you can get blood in there…