Isn't "optimal" subjective? What if the person is on a hill, or on a flat, or in a terrain trap (gully) or steep creek trap, wouldn't that change the 'optimal' antenna to use?
I suggest, if 3 antenna, there should be a protocol that allows devices to transmit on each antenna in 3 separate transmissions, basically allowing the receiver to pick up on whatever transmissions it receives. They probably do this already for all I know.