This is my experience of watching wingers try pump and then my own experience winging and then pumping while winging. Winging messes with your pumping abilities and throws your low end sensitivity.
I think this is because you end up trimmed incorrectly for pumping. Weight too far forward.
Moving your feet back so that you are perfectly trimmed is the most important thing, meaning you can glide more for each pump, and maintain the same altitude. Too far forward means your pumps are mostly getting your own body weight up to even, rather than gliding at the maximum potential of the foil, and using the pumps to gain height.
I think this is more fundamental issue than “stay high on the mast height”. Continually riding low on mast is a symptom of bad trim and not able to maintain height.
More about Foil Trim - how to get the balance right