LTC4125 efficiency

I have a wireless power system using the LTC4125 Tx and LTC4120 Rx. Both use the standard application from the data sheet. I'm attaching a copy of the output and input waveforms.

Yellow is the TX output and purple is the Rx input. My questions are, 

Is the flip flopping of the Rx wave caused by the ringing on the Tx wave?

If so, since I can't find a spice model for LTC4125, Is there a way to use capacitive feedback instead of resistive feedback to clear this up? What capacitor values would I use?

Thank you ~V