Not a dumb question at all, but you need to elaborate alot more. What's your reasoning? Are you feeling like you're not getting enough growth from flat press? Does flat hurt your shoulders?
As far as the carryover, I think that's completely individual. Personally, whenever my incline goes up, I see little effect on my flat; however, as my flat climbs my incline goes through the roof. Other lifts that are more directly similar to the flat bench will almost guarantee a carryover though...such as floor press, pin press, board press, etc.