This is the same essentially as the trackman "stuff" . . . if there is a divot the club is traveling down AND OUT . . . period . . . so down is "swinging to the right" . . . the right of "something" . . . maybe not the correct something but to something. Lowpoint . . . ala hulu hoop in the ground.
Down and Out to a degree consistent to the angle of the inclined plane being employed (assuming you are on a plane). The flatter the more out , the less down the steeper the more down and the less out.
There are Angle of Attack, Arc implications associated with plane angles and shifts. So though the actual plane angle being employed may be said to be irrelevant to the measurement of ball reaction its still part of the overall geometry and anything but irrelevant to a golfer, especially one trying to aim his circular clubhead orbit in some manner....unless he choses to trace circles with his clubhead but then he'd need to change that circle for each club , for each ball position, for each release point, for each plane shift etc. Far easier to just use the straight plane line. Or the alternate method the Aiming Point.