Light on the line...very little handle pressure through the turn itself is what he's telling you, it is wrong to be light/pressureless after the turn and into the wakes (as the line gets shorter you need to start edge changing in the wakes)... this is only where a person should feel any load/pressure, or another way to look at it is he's telling you that you are impatient at the buoy and forcing the turn...or your loading at the ball...there are lots of ways you can create 'patience/light line/' through the turn, Marco softens his knees, this creates more time letting the ski finsh the turn and inhibits him from forcing a 'pulling' action too soon...pressure in the pull "behind the boat" (a term which is a misrepresentation of applicable area to "pull") is an absolute, it's when the application of pressure that is instituted in your path through the course that affects your skiing results.
Marco you are so right with the soft knees and lowering stance is a superior position to be in the pull rather than a tall stacked position...a lower CG will always require less effort on a skiers part in comparison to a taller straight legged position...Does a person stand tall during a tug of war? Worlds strongest man comps, always low in any pulling comps...