From the back of the bike, the right side pipe is where most of your exhaust leaves. When I had the straight shot slip ons, I had to paint the inside of the left pipe black to match the right side because there was hardly any exhaust leaving that side. . .. .
Do yourself a favor and change that crap out to a true dual or 2-1 setup. Put on whatever makes you smile when you start it up. You're dealing with someone else's backyard hop-up that will never work well. There are true dual kits that allow you to modify the stock header pipes and add slip-ons or you can buy an entire system.