Simulated on FEMM.... Need Reviews.....

Hi friends. I have simulated a Magnetic Circuit on FEMM(snapshots posted below). I want to understand the effect of the foll:
1) The material of the holder.
2) The Thickness of material in different areas in the circuit (i have varied the thickness to vary the saturation area)
3) Selection of Steel based on the Permanent Magnet Material Type(SmCo, AlNiCo, etc).
4) Selection of steel based on its B-H Curve.

Thanks....