The tab works a bit like a fixed trim tab. By pushing it down you will create some lift at the back of the boat, however this can make the front of the boat stay down and plow water and cut waves more than it rises over them.
The opposite happens if you pull it up, the bow will rise and it will go over waves better but the back of the boat will ride deeper in the water.

If it is level now and you like the wake it is probably fine where it is. If you want the wake to be smaller and firmer you could try pushing it down in small increments until you feel the bow plowing water at speed.

I think the surfing crowd likes to run them up and have the back end of the boat low to shape the wave more.

Hope that helps.

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