On occasion when I do top not been a problem. Not been much of a problem when I am getting fucked (95% 0f the time) but I am told I do a good job of milking the guy to help it along.
I began as a bottom and then I realized I liked it more to be a top, never looked back haha. However, it did take me a while to get there, lube is a must. Also, every rectum has its limits. If you pretend to begin with an XL cock, I wish you the best for you have a loooong way ahead of you. Buttplugs help, but what does get you there, to really enjoy it, it's both being turned on by your sex partner.