Polk Atrium 8 distance from another?

Just picked up a pair for Polk Atrium 8 outdoor speakers and I was wondering what is the optimum distance to place them from one another out in my covered patio.

I am using a Yamaha RX –A 760 receiver and going to be using them for Zone 2 which is L and R terminals. Is there a thumb of rule on distance for two outdoor speakers? Can it be bad if they are to far from each other or to close?

Thanks.