Also, take into consideration where the PS is located. Since it skimms close to the surface(where most of the PT sits, you want it close to a intake on your filter or sump.
there is a natural cycle of how the water flows in your tank, make sure your skimmer isnt in a "Dead" spot on the surface where there is little water flow twards it(like water being sucked away from it)or a "Active" area where surface water is being pushed away from the skimmer.
try shutting off your skimmer, leave everything else on in the tank, powerheads, filters, and anything else that moves water...then take a styrofom(the non-bio degradeble type) and put it in the middle of the tank. and observe which direction piece goes, try it in different places too, try to find a area where the piece always goes...then stick the pump there...however it will change the water direction when the skimmer returns the water to the tank.