If it didn't work, they wouldn't have made it, it was designed for a specific bike, most of which are fueled from the ,"sitting on the side stand" position, which will allow it to fill the left side. As most bikes have a left side stand.
If the tunnel is flat, then there is plenty of room for fuel to flow to the other side. At least an inch, at the highpoint, tapering to 0 at each end. That gives a pretty big "slot", much bigger than a gas nozzle
here is one in its natural state. sorry about the crummy pics. If I remember right it came off an Ariel or AJS. I ran it for a while on a straight leg pan frame . It fit over the stock mounts, and sat level just a little above the support bar. did not look too bad.