As well as the magnetically induced currents in the substrate, any capacitance to the substrate will have resistance in series with it, so thst would be a resistor in series with the Csub component in the model shown above. As Stefan points out, this resistive loss can be reduced with a patterned metal1 shield (at the expense of somewhat increasing the value of the parasitic capacitances, but it is worthwhile). I think that it is probably not worth guessing the form of the equivalent circuit until you have the model, because that will depend on the modelling tools used as well as the number of terminals on the inductor ( if it has centre taps, or other taps and maybe additional windings). I generally use two models, a complicated one with hundreds of components in it that my field solvers give me as a netlist, and also a simple one with about 5 or 6 elements, that I draw a schematic for, and fit to the complicated model at the frequency of interest.