From the technical information, here is the path of air flow based on manual settings. Perhaps this will help you as you experiment. Closing the registers on the front passenger side may help, but also may frost the passenger window in the winter.
Center defroster, side defrosters and side registers
Defrosts the windshield through the center defroster, side defrosters and side registers while air is also blown out from the front and rear footwells register ducts
Air blows out of the front and rear footwell registers ducts, and side registers. In addition, air blows out slightly from the center defroster and side defrosters
Air blows out of the front center register, rear center register, side registers and front and rear footwell register ducts
Air blows out of the front center register, rear center register and side registers
Face is full flow to the front center, rear center and side registers. So closing the front center and front side registers may cause full flow to the rear center. So varying the position of the rear center louvers would modulate air flow, while raising or lowering the temp settings would affect the rear seat.
Bi-level is air flow to the front center, rear center, side registers and front and rear footwells. In the winter, this would be nice as heat rises and heat from the rear center and rear footwells would bath the area in heat based on the temp settings.
Good luck in your experiments. In the summer, settings would be slightly different as cool air falls rather than rises, so you'd want it on your head/face rather than your feet.