Doing a fresh water wet test on my 125 and since my Wave Box was purchased used it came with no instructions. I'm curious is it better to place it high in the tank with the top close to the surface just short of vortexing air into it or placing it lower?
there is a blue line on the front of the box, that is the still water line of the tank. Install the box so the water line hits the blue line and then slowly dial in the wave. It can be frustrating to get it dial in. Small turn wait, small turn wait. Once a wave starts then you will need to fine tune it to get maximum amplitude on the wave.
If your blue waterline isn't visible anymore, it's about an inch from the top of the unit. On my 120 it makes about 1 to 1.5" wave but a 125 is longer than a 120 so you can probably make a bigger wave than I can. I've seen them placed in back corners, front corners, and sometimes on the back facing forward, like chingchai's from thailands tank.
I personally have mine in the front left corner and my corner overflow is in the back right corner. It's best to have your rock off the glass so the water has a race track. Here's a picture from a couple weeks ago, you can see the water line on the front of the glass to see the size of the wave it makes on my tank.