You bring up a good point.  The contact between molar teeth is nearer
the chewing surface than the gumline.  Esp. if there is gum recession,
it's not unusual at all to have some space between the teeth near the
gumline but a decent contact near the chewing surface.  Food impaction
from the side (horizontal food impaction) is generally less damaging to
the gums than vertical food impaction (through a weak contact).  So
there may well be nothing wrong with the crown.
    Even so, I would check for what we call "plunger cusps" from the
opposing tooth contacting near the space.  Sometimes I'll see
improvement by just taking an abrasive stone and rounding the contours
of any opposing cusps.
    As far as re-doing the crown for horizontal food impaction, it could be
done--by overcontouring the crown where it faces the adjacent tooth in
the food impaction area.  This would decrease the area available to pack
food in.  However, this could solve one problem and create another, as
overcontoured crowns tend to be irritating to the gums themselves.  If
your dentist is diligent and honest, he should be able to speak to you
in terms you can understand as to what might be causing this problem,
and what might be done to improve the situation.  If there are no good
options, he preferably should be able to explain why, esp. in view of
the fact that this problem did not exist before placing the crown.

Steve

sounds like maybe you have gum disease...maybe some bone loss