Size Issue?

Brandis
I know what most of you might already be thinking, but this issue is that my partner is a little too big (for me I believe). Some positions, it hurts. His favorite is from behind at a particular angle. This used to be my favorite position too, but now I'm always a little nervous for it because I know  7x/10, it'll hurt or be uncomfortable. When I tell him he's too big, he thinks I'm lying to up his ego too much. Help? Tips? Ideas please?