Hi Saeed,
The question is so general and I am not sure what sort of setup you are using. In general, note that SBR+ is an asymptotic solver and suitable for electrically huge scatterers. If it is used properly based on SBR+ assumptions, we get very good agreement with full wave simulations, in much shorter time!
If you'd like us to investigate your design, file a support ticket through customer portal. If you don't have access to portal, you may share some more information here and we will help within the scope of this forum.
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