You are getting about 7574gph, It all comes down to position, tuning and tank layout. That sounds like a fairly long frequency for that tank. You need to tune it until you get one continuous wave, cresting on one side, trough on the other, each tank has one ideal frequency and I would expect it to be between .6 and .8 seconds on your tank. The wavebox should have a clear shot to the far side of the tank. End overflows will reduce wave height, center overflows are ideal.