The divider might work - but if the mare can choose where to go you have to make sure that the gelding cannot get trapped. Each section should have two open sides, so the gelding can get away.

Enough room is the main part. You could also try to feed outside on different sides of the shelter. That way the gelding can get out of the way.

As mentioned, it is totally natural. My lead mare will go from pile to pile - and everybody else just gets out of the way - especially the stud.