Men are less likely to report sexual assault and rape against them than women are, for a number of reasons. One being that rape is defined as being penetrated against your will, and not being made to penetrate against your will.

Any study that counts convictions, or even complaints, it going to underestimate male victimhood.

You need to look at victim surveys to have any hope of estimating how many man are raped, and how many women rape.

See my other post in this thread for details on that.