Problem in force calculations

["Dave Squires" <djsquires@xxxxxxxx>]

David,
I have a problem with force calculations in a simple
permanent magnet simulation. The setup is to have
two permanent magnets set up in a opposed arrangement
with + to + (N to N) and an intervening layer of
soft magnetic material like supermalloy or pure iron.
This material would be placed against one end of one
magnet. The other magnet in repulsion is brought
closer and closer to the iron. There should be a point
where the force switches from positive to zero and then
to negative. It will reverse direction from repulsion
to attraction at some distance. I don't see this with
FEMM no matter how close I get. 
Any idea why this would be the case?

You can do this test on the bench with a couple of 
NdFeB magnets to prove it to yourself. Just use an
equal thickness of magnets and iron or steel.
So in this case FEMM does not seem to reflect reality.
How come? Is there any way to fix it so it gets the
right answer? Or am I doing something wrong?

Thanks,
Dave Squires