Pointing the fan at the caps is mostly for PAR output and bulb life. Any air movement should help with heat, but pointing at the caps probably won't help as much as pointing down the length of the bulb. One thing to keep in mind though: some bulbs (ATI's for instance <according to Grim Refer>) have their PAR drop when you cool the bulb instead of the endcap. However, if you put some sort of vent in the top of the canopy, cooling the endcaps should be sufficient all around.