My fans both blow in and directally on the surface of the water, I have found that is the most effective way of cooling my tank. I might add that I have a temp controler that kicks the fans on and off to control the temp.
When it comes to cooling a tank there are a couple of things to consider. 1) is removing the humidity as fast as possible. You have to do this to induce more evaporation. 2) removing the hot air and exchanging it for cooler air.
Evaporation causes the object that the vapor is leaving to be cooled. This is why we sweat. Air can only hold as much water vapor as barometric pressure and temperature will allow. I do not know the specifics on this I just know it to be a fact. The higher the pressure and warmer the air is the more water vapor it can contain. This is why a thunderstorm will follow a high pressure zone and as the cooler low pressure air moves in the rain begins to fall. So removing the humidity to induce more evaporation is definitely necessary.
the cooler you can keep the ambient air the faster you will be able to reduce the temperature. This is very obvious.
Now a third thing you need to consider is the power of two forces... pushing and pulling. The force of pushing is much more powerful than the force of pulling. An example of this is with your pumps. You can somewhat restrict the flow coming out of your pump and the force of pushing will somewhat over ride the restriction and like with your garden hose it will squirt the water. But if you take the same pump and restrict the intake the same amount on it you will dramatically reduce the amount coming out of the pump. Another thing is if you take a syringe and push all the air out of it and place your finger over the end of it and pull the plunger you will notice that you can pull the plunger all the way out with very little resistance now if you take and pull the plunger to its maximum and try to push it in you will not be able to do it. The force of the air pushing on the inside of the syringe will be much stronger than you are.
I suggest that you face the fans pointing into the stand with enough ventalation in it to let the incoming air escape but not so much ventalation that it just falls out. You want to be sure there is a current of air in there. And you want to maximize the surface area of your sump water to give it the largest amount of area to evaporate from AND to give it the most contact with the coolest dryest air possible to disipate the most heat and water vapor possible into the air. Like whiskey said it definitly helps to have the air blowing directly at the surface of the water but not so much that it blows salt all over the place.