Just got my 30" Ray II and I have the same issue--the maximum opening of the legs doesn't really fit the ~5/8" rim of my 56 gallon. It is ok, but the clamp seems to be opening too far and you can't really use the screws to secure it--it just pops out. I'm kind of disappointed the legs don't open wider--and I'm worried they're going to break.
That said, the light looks good and is a big step-up from the single fluorescent light that came with the tank. We'll see how the plants like it over time.