on which nodes do I put the VIN?
without it I get a flat reading at -300V on the AC analysis
(trying to reproduce your graphs)

I got bored in my physics class so I read ahead, and whadaya know I stumbled on capacitive reactance. I messed around with some equations and finally understand how a first-order crossover works, yippee!! though its not exactly 6db slope... 6.03 or something I don't remember.

I'm starting to make a VB app to visualize the design of simple AIM-Spice models... I'll let anybody know when I'm finished.