Similar to above suggestions...I added a thin strip of black 1/4” acrylic to regulate the weir overflow on my Eclipse L installed on a 40B QT. I have some small acrylic squares on the inside that I drilled and threaded for three nylon screws to clamp it in place. Had I known this was going to be an issue I probably would have modified the overflow itself similar to the water height adjustments on many sump designs. Otherwise I really like the Eclipse overflow.
Incidentally, I placed the templet as high as I could on the inside of the tank to drill. I typically drill from the inside out just in case the breakout causes a chip in the hole edge. Much better to have that outside than inside and potentially cause a leak.