OK, I see. In the MOSFET with Diode model, the switch-on losses for negative currents are for the diode-part of the MOSFET only. With this approach I can not model the FET during hard- and soft-switching (model can not differentiate between the turn-on losses caused by the diode and by the output capacitance). Therefore, I will use the MOSFET without diode and use a separate diode in parallel to model the reverse conduction mode of the GaN FET. I can then add both losses and the model works for both hard and soft switching.
Thank you for the support