Get it all the way to the full mark, with the bike totally upright. I belong to 2 other motorcycle forums and 2 scooter forums. (Almost) everybody seems to have gotten the idea that running an engine with the oil level at the halfway point is the way to go. BULL. Fill it all the way up. IMO, the Rebel does not hold enough oil anyway. My Vulcan 750 holds 4 quarts, almost as much as a car engine.
I don't advise overfilling it. Some engines you can overfill slightly without a problem, some you can't. I routinely put 6 quarts in my small block Chevy that was designed for 5 quarts without any problems. But I've built and rebuilt so many small block Chevys that I know there is room in there for 6 quarts. Never had a Rebel engine apart.
Another oil related issue. I don't recommend using any oil lighter than 10w40 in any internal combustion engine. These super thin oils will cause an engine to wear very fast, they have very little film strength, and can easily break down and allow metal to metal contact. I use 20w50 in all my vehicles, including motorcycles, because I live in AZ, where summer temperatures can reach 118 degrees. Jerry.