Plotting Multiple Eigenmodes in HFSS

Hi All,

I'm just starting out using the Eigenmode solver in HFSS. I have a simple structure that consists of 4 alumina rods in a square lattice in air. When I attempt to find the resonant frequencies of the structure, I get different results for the modes depending on how many modes I specified HFSS Solve for. Eg: When I solve for 1 mode, my first mode resonant frequency is around 60 tHz, but when I solve for 2 modes the first one is 59 tHz and the second mode is 63 tHz (approx values). My understanding was that the solver progressively solves for resonant frequencies above a minimum specified frequency depending on how many modes you specify, but these results do not seem to jibe with that notion.

Help?

Thanks