We don’t know what experience you have had and how did you reach to that conclusion but in my opinion it is only fair to say that if such a situation exist then it is only because…
- They are better performers
- They are better communicators
- They are more confident than their male counterparts
- They are proactive
- They are good at managing stakeholders
Onsite assignments are not simple. Clients are very aggressive, demanding and critical. They do not entertain non performers hence it is not practical for any manager to do any gender bias while selecting candidates for onsite assignments.
Same goes with performance rating, why on earth would someone give higher rating to someone just because of their gender? At the end of the day, it is a business decision and no one ever wants to give higher ratings to someone who is not able to perform well.
Last but not the least, do not forget that not all managers as males, there are female managers as well hence there is no room for any bias anyways.