HFSS Global Variable Problem

Hello,

I am simulating a planar antenna on a substrate that does not have a ground plane. I am changing the value of the permittivity and loss tangent. When using the optimetrics option the values of s11 gradually change as I change the material properties of the substrate. When I directly input the values for the material, instead of using optimetrics, I get significantly different results as the material and antenna become less matched. When the material and antenna design are matched for the frequency of interest the two methods have very similar results.

I also changed the material properties by changing the global variables values that I used in the optimetics analysis (without running the optimetrics) and the results matched the optimetrics results.

TL;DR
When using global variables to assign the material properties of a substrate and when directly entering the values of the material properties I get different results for s11. As the material and antenna become less matched the difference gets larger (when matched the difference is very minimal). I am simulating a planar antenna on a substrate that does not have a ground plane.

Thanks in advance for any help anyone can provide!