FWIW- I ski with, and boat judge a number of people capable of -35, and usually see one or more of the same things when they are having trouble at shorter lengths. I think you nailed it already- holding accelerating lean/load after centerline adds down course speed... Visualize you can hold direction at 90 degrees to rope tension (most of us can't)- a tangent to the arc of the rope. As the line shortens, past C/L, the tangent starts to have a larger down-course somponent. (At -38, halfway C/L to buoy, (45 degrees) assuming you maintain load at 90- about 7/10th of your effort would be in the same direction as the boat...) Watch video of the pros- their edge changes are very quick- almost violent, and are rarely much after C/L.