Both Manley and Ruttner advocate stationing large hives containing desirable genetics around the mating yard. I think its simply a case of the more effort you put in to have your own drones impregnate your queens, the more likely it is to be so.
I can't imagine the bees use a rulebook that disqualifies drone on the same property. All else being equal I'd have thought that being nearby increased the chances without limit. I'd be interested in any proper studies that show things are otherwise.