I think the "transition" or "conversion" is complete when you can no longer cum without something (in my case big) in your ass.
and cumming without touching yourself i.e. "no hands" while you're getting fucked. I know when my wife walked in on me once and saw that, she commented, "Oh, my God! You really are a bottom now!". Who was I to argue? I find sometime my sissygasms are brought on when I feel the top emptying his ball deep in my gut, keeping the head pushed up against my prostate. I almost always give up my load when that happens. I can't help it.