Prostate location

If I have a 6inch erect penis, how many inches further is the prostate?

Location of prostate is not related to length of penis. https://en.wikipedia.org/wiki/Prostate

I’ve recently discovered by reaching around with a soapy finger in the shower that my prostate is much closer to my anal opening than I ever imagined and much more accessible for stimulation while my other hand strokes my erection. Quite tantalizing and gets a quicker result. At 81, I’ll take anything I can get.