The larger ones open the rectum up and allows the penis to travel through painlessly. The smaller dicks tend to zero in on the painful parts without opening the outer rectum. This is why larger cocks feel good while small cocks just hit the inner walls. My first gay experience was painful because he was only 5.5" and cut. I bled for a week while going to the toilet. After opening it up more with a dildo, I met a guy in the gym who was hung in the 23rd ST Ballys in Manhattan which had lots of gay men. It was a wonderful second time as his cock opened my ass up and prepared my inner walls for his head to slide through. He was also uncut which made it glide in and out of my ass. This is why I only do man to man sex with uncut men.
Also, I am unfortunately cut and am frustrated about the way it happened to me but I have described it in another post. Women tend to use lots of lube for the cut cocks and they should. I slather my cut cock with lots of Crisco oil until every last inch of my 7" is covered.