Rich that is an excellent description!
Another way of thinking about it is that the downhaul/tack
line lets you adjust how deep or shallow the genaker is 'cupped' while the sheet controls the angle (simplified but an ok starting point IMHO). The size of the gennaker is fixed, so is the height of your mast, the tack
line lets you cup and uncup the sail to fit conditions. Remember back to your experiments with aerodynamics as a child with your hand out the window of a traveling car? genaker adjustment is the same thing don't make it too complex.
