Tuning matches for admittance but the corresponding reflection coefficient is not expected

Hi everyone, I faced a problem about coil tuning. I followed the official instructions from Sim4Life to tune the coil to 50ohm and the highest peak of admittance is now at the target frequency. However, when I check the reflection coefficient of each channel, it is not closed to 15~20dB. Here are screenshots, please help me and thank you all in advance!

If you click on Network Analysis in your Analysis tree, what is your Reference Impedance?
It is set to 50 ohms by default, but you have change it based on the Input Impedance for the coil before plotting the S11 curve.
Plot the complex Input Impedance. At resonance, the imaginary part will be zero (the circuit is purely resistive). So at the desired resonant mode / frequency, you should find the corresponding real value, and set this value as the reference impedance to plot S11.