Problem with SIW cutoff frequency in HFSS

Hi everyone!
I'm starting to handle the software HFSS.
I have to work with SIW(Substrate Integrated Waveguide).
Just to know how to handle the software, I designed a rectangular waveguide, and the results were like I spected. Then I designed a "SIW" model, but with grooves, instead of vias, and the results were satisfactory too.
But when I designed a proper SIW model, the cutoff frequency wasn't the expected.
Any suggestions?
Thanks

Cutoff is not expected? What is your baseline/reference? some books or paper?

The diameter and density of the vias decide the cut-off frequency. So you can tune them until you get your expected cut-off