From my experience dip is of such a random nature the programmers probably didn't bother adding it.
At the club i used to work we had two warriors.
One aircraft had the adf loop under the belly between wings, this gave loads of dip ( i think the wing blanks off the signal) and the other under rear fuselage clear of the wings, resulting in no dip.
Also rarely seen any dip in Cessna but loads in Senecas.