I don't think I've ever seen an adequate explanation for this. Memory Alpha says the uniform tunic didn't fit him to start with so they were forced to put his comm badge up on the gray portion of the uniform for a few episodes, but I can't see why the uniform not fitting him would dictate where the comm badge goes. I mean, Riker wasn't forced to wear his comm badge in a different spot when he wore Sisko's hand-me-downs in "Generations". How is it that the comm badges were fastened to the costumes anyway? 
