ummm,if your talking about an oscilating fan then you want it aimed at the upper portion of the plants.u do this for several reasons.to give your plant strength "just like if you started lifting weights,your going to be stronger than if you didnt,the fan is that dreaded weight set" .your plant will use up the amount of naturally available co2 in the room through its leaves pretty quick,to combat that you have your fan to keep the air moving. 3 just remember your trying your best to re create nature,wind is a natural part of nature and is a there for a reason.