Mock-up of my new tank
The answer to your problem...I didn't use the whole chain tensioner. I just bolted the wheel to the back piece, but I had two. You may need to just cut half of the chain tensioner off so it is about half the heighth. In doing so, you can slide it back much further where the frame is wider. My bike runs great and no rub.
Just two tanks I fab'd up a couple days ago.