[HFSS] S21 parameter problem

Hello

I'm trying to get S21 value using coil.
I did an experiment using vector network analyzer(VNA) and found out that S21 peak was found at 12.3Mhz.
but using HFSS simulation the peak value was find at 8.8Mhz.
I attached the file and can you find the problem the difference of measured value and simulated value.
Thank you!
Any comment is okay!