Quality factor - etch angle

Hi,

I'm simulating the Quality factor for planar pcb coils. When I'm measuring the Q, it seems that it always lies in between simulation results for zero and finite thickness.

-What is the cause of this ? Does it has to do with etch angle or is it due to etching irrugaliraties or something else ?

-If it's the etch angle, which sim software can be recommended ?

Thanks in advance,

note: good answers will be rewarded with points/helpfull ;)