I would add to @Than_Bogan comment that you can be stacked and be flat on the ski, the result is no speed building and even at 15off , it will be hard to run the slalom above 32mph. So stacked is great and adding some leverage and building speed is the beginning of the key, plus building speed at the right spot is best, not after the second wake but to the CL is the best.
And as a beginner, crossing the wake with angle on the ski is so much safer than ski flat.....that is a mental game.
I am a 32-34mph skier 15off on public lake and we have extremely rarely glass water so we have to overcome the reflex to stand in a denfensive way....which is hips back, like Marcus Brown shows it on his video "Athletic stance" . And we have to get ride of that muscle memories and it is time consuming, I know by experience.