Different programs handle rigid elements differently. In CAESAR II, the stiffness of a rigid element is determined by holding the ID constant and increasing the thickness by a factor of 10. The result is that an 8" rigid is much stiffer than a 4" rigid, but much less stiff than a 12" rigid.

Other programs simply multiply E by 10 or 100, so all rigids have pretty much the same stiffness.

While we feel our approach is closer to reality (and therefore more accurate), it really shouldn't make a difference unless the system is significantly sensitive to the rigid element.

Test this out yourself - remove the rigid and see if the three programs agree. Build the model up from there.