I get what you are saying but just by looking at it, the current belt seems to be a tad wider than the one I had in there before (Dayco top cog vs. Gates bottom cog). It also appears to sit flatter in the groove. Could be just the outside of the belt, not sure. Again, I've read where people suggested to go with a Dayco top cog belt over other brands, perhaps this is why.
Regardless, there does not appear to be much extra room for a wider belt to sit in the pulleys without riding up on top of the groove.