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OK here is the reason for a perforated standpipe and how you can make it work with the wavebox.

If there were no wavebox then tuning the Herby would be easy, just slowly adjust the gate valve until the water level in the overflow is just right to give no sound.

Now the perforated standpipe is to give you a margin of error where the Herby will function properly whether the water level is a little higher in the tank (top of the wave at the overflow box) or a little lower in the tank (bottom of the wave at the overflow box).

You want the bottom of your standpipe to be full at all times, to have enough water pressure to to this the water level within the overflow box will have to be x number of inches above the lowest perforations. The exact amount of inches will depend on the amount of flow through the overflow, the diameter of your standpipe and drain pipe, and the surface area of your perforations. But lets say 6" above the bottom perforations in the standpipe.

You also don't want the water level in the overflow to be too high or it will start to come down the emergency drain and make noise too.

By having a large height of perforated standpipe, you can set the water level in the the overflow box to about the middle of the perforated area. When the wave is at its lowest, less water flows into the overflow box, the water level in the overflow drops a bit, but it is still high enough to provide enough pressure to completely fill the bottom of the standpipe. When the wave is at its highest, the water level in the overflow goes a little higher but still not high enough to go down the emergency drain.

You can do this with no standpipe at all, however there are two drawbacks. Anything large getting into your overflow can hang up at the gate valve and partly block your flow. And the drop from the overflow weir down to water level in the overflow will be high enough that it will make some splashing noise.

In addition using a standpipe allows for a permanent area of protected water to form in the overflow box ie. a non-lighted refugium which can be a benefit for diversity.