permanent magnet (Nd magnet)

I designed the nd magnet.

In magnetic flux conservation 1 , the z axis was set to 0.5030T.( Nd magnet)

In magnetic flux conservation 2, air domain was set to relative permeability. (Air zone)

Infinite element domain1 is set at the boundary.(5mm edge layer of air zone)

but if the air region size is made different, the magnetic field value coming out of the center of nd magnet surface becomes different.

1. I set an infinite element area, but why does the value of the magnetic field change?

2. Is it because the internal meshing has changed?