If your current noise model is correct (in my HSPICE mosfet manual I found that you can model thermal noise generation in the drain and source resistors as two sources, inrd and inrs).
The following equations calculate the values of these sources:
inrs = sqrt(4kt/rs)
inrd = sqrt(4kt/rd)
then, 'rs' and 'rd' must be drain and source resistors, the same should apply on your 'r' parameter,