<...  Doing so would also result in
>another 1/4" opening facing down on the back side of the hive . . . Do
>the bees use both?  Is there any problem with the bees ability to
>guard these openings or other bees trying to rob, now that there are
>three "largish" opening in the hive?
>
>
>-- John Taylor --
>Wild Rose Creek Apiary
>Southeast Missouri
 
Shifting one of the supers back about 3/4" leaves a 1/4 - 3/8" opening
along the front, at the top of the underlying super.  There is no opening
created at the rear of the hive, due to the thickness of the super walls.
(The rabbet at the upper edge of a super makes a thinner edge, allowing for
the opening at the front of the hive... ? ...well, try it and you'll see
what I can't seem to describe.)
 
Never had any robbing with this arrangement.  It is used during the height
of the season, when the colonies are populous and forage is plenty.  In
some regions where robbing is a problem it might require some caution, but
strong colonies such as these are not apt to be robbed anyway, and
certainly not during a honey flow.
 
This is sometimes referred to as "staggering the supers."