Difference between simulatings

I have simulated the same structure ( phased array of 8 dipoles grouped in ring) with Matlab, Nec and HFSS. The problem is that radiation pattern for hfss is totally different from the others. Theoretically, results should be as matlab and nec perform them. But what could be the reason for this difference ?

I think there might be different reasons, one of them could be the method used.
NEC uses MOM while HFSS uses FEM; what kind of method did you use in matlab?

I have only simple null-steering code which is not product of my own. I could not see any hints of the method in a code.