The POT on mine is "tall" but not "deep"; i.e. the adjustment screw is right at the top of the little "tower" - take a look at this image from QFM which shows the POT on an angle at the far left:
http://mywebpages.comcast.net/qfm/racing/img/nimh3.jpg
The adjustment screw on mine is at the surface of this, however, it sounds like yours is either a different design somehow and the the adjustment is recessed, or that it's defective and that the adjustment is missing! This was a brand new unit, right? Where did you get it?