The root of the problem for most when pumping is that you’re standing too far forward. This is what all wingers do, because of the big pull of the wing.
FD doesn’t help because you stand even further forward
So in both cases when you pump, you push the nose of the board down, instead of jumping up off the foil.
As Gwen says, the feeling is jumping up, not pushing down.
So get on foil (ideally behind a boat), and keep shifting your feet back until it feels a bit loose and sketchy, that is close to the sweet spot. (you could do this on the wing, but it’s hard to stand in the sweet spot with so much power)
Once that trim is right, slow the boat down, let go and try pump. The foil will feel super firm, and you can start to do the “jump” that Gwen talks about.
This is also the place to stand when you’re gliding downwind, on the FD, wing, etc, as this is also the max efficiency, any further forward and your drag increases like crazy.