My advice. Don't talk about it before after or during sex, some other time is best. If you bring it up, find a positive way to do it so you do not make him feel inadequate.
As for the talking, try some sex talk when you aren't having sex, make it fun, a game or whatever. Tell each other some fantasies. Then you can bring your desire for other positions into your fantasy talk.
But becareful not to make him feel inadequate in general.
NO, it is not unreasonable at all. You both deserve to be satisfied and he will actually feel better if you are happier. The communication will likely bring you closer together once you get through it.