is there a trick to matching return flow on a herbie?

[04scoobysti]

The only problem i could see (looks like you have a gate valve) is that your herbie is located in 2 different overflow boxes. That might make it more difficult to tune. Also the wavebox is running in the same direction as the overflows, this would make more noise if the wave trough drops below the overflow teeth. Almost a surge of water when the wave crests back at the overflow.
My 2cents.