in simplistic form, pressure is just the flow rate divided by tubing area, so the smaller the piping, the greater the pressure.
however, pressure in this case isn't the important thing, pressure is only mentioned in the context of "not much flow", as in "i put my hand in front of the return nozzle and there's not much pressure".
reducing the size of the pipe would certainly increase the perceived pressure from the return, but the real question is how that impacts the GPH delivered given the static head pressure, and now the added friction/pressure from the smaller pipe.