Here is the link to the article where I read the fans should be blowing over the ends of the tube with the logo: Reef Aquarium Lighting - T5 Basics Good basic information.
Here is what was said specifically:
"T5's have what is known as a cold spot where the temperature determines the gas pressure inside the lamp. Some, but not all of the lamps have a dedicated cold spot which is at the label end. On other lamps regulating the temperature at either end will give you top performance but it is good practice to just cool the label end of all lamps to remove any doubt. Using a fan on the center section of the lamp will quickly over cool the lamp which actually will hurt performance more than not cooling at all in the case of the normally driven T5's. T5 VHO systems which are T5 ran on Ice Cap ballasts to overdrive the lamps must be cooled. Not doing so will lead to early lamp failure which is typically a crack at the reflector clip. The Same rule applies to cooling HO or VHO T5’s, don't cool the center of the lamps.