Poor fresh air flow

The (cabin) fresh air flow in my '93 EX is not as good as I'd expect unless I crack the sunroof or a window. According to my owner's manual, the air is supposed to flow over the rear seat (?? between the seat and rear window shelf??) and out through vents somewhere below and at each side of the trunk.

Anyone experienced the same problem? Where are these rear vents? Did yours need cleaning out?