Since you are referring to the angle (Edit: you actually didn't say angle, but you said there was a certain way that he strokes. I think you're referring to the angle.) I suspect that your partner is hitting the wall of your anus. There are two components to this problem: your position and his angle of entry.
As your position changes, so must his angle of entry. For example, if you are standing up, you can see how he obviously couldn't enter straight in, with his dick parallel to the floor, because he'd poke right out your belly button, right? He would have to enter in and up.
Now think about that in relation to the position mentioned by a previous poster above, lying on your stomach with legs together. In that case your body is in a similar position as when standing, so the angle of entry from behind is perfect. The penis will slide right in with nothing getting in the way.
Another way to create a clear path is on your back with knees pulled up to your chest.
The best way to deal with this is pratice. Tell your partner to use his finger and feel inside you. He will immediately tell that his finger will go in at a certain angle. That's the same angle he needs to use with his penis. Then he must remember that angle when things get hot and heavy, because if he shifts, he will start pounding the anus wall again, and that hurts. The best way is to actually leave his finger in there and the slide his penis in paying attention to the angle of his finger.
I'm not sure if any of this makes sense. I wish I could draw a picture. As I've said before on this site, buy the book "Anal Pleasure and Health." It is written by a doctor, and it has pictures explaining all of this. It makes perfect sense when you see it.
Good luck!
