Don't forget that one of its jobs is to collect overflow incase of overheating. If you are away from home and your engine overheats and there is no room for the overflow to be collected you will lose it, and and most of the time you wont notice its flowing out until you come to a stop. Makin the reservoir small in not a good idea. I don't recomend running the bike with too little cooland. You might be able you move it back some by moving the battery tray back a bit. Maybe you can get a resevoir from a different model. How big is this horn anyway?