I had an experience like that a couple of years ago. The woman was 5'1" mid 40's and supposedly she was not fucking some porn sized cock every night or any for a good while for that matter.
I am about average in lenght, 5" but do pretty good on girth, enough so that a few women have commented about my "fat dick" or call me "well endowed".
With this woman I could not tell I was entering her, it felt like and I assumed what was happenig was that I was somehow sliding under her pussy, the area above it where her clit and pee hole is is what felt like and i assumed was the entrance to her pussy.
She was the only woman out of a few dozen who I literally could not tell I was inside her, others were various degrees of loose but I could always tell I was inside them.
She was pretty matter of fact about how she didn't orgasm, I did not tell her but I sure did not either.