Simulating floating bench power supply stability

[Chosee]

Hello

I have read around a lot, and i can't seem get my head around simulating the loop gain of a floating power supply. I have tried a bunch, but what i can't figure out is how the 'ground' being the positive of the supply output affects the loop gain measurement. Can someone help me with a good way of simulating loop gain in a floating power supply. How to hook up the ac stimulus correctly for instance.
I have attached the design i am trying to simulate here.

Thanks a bunch!  :)

[udok]

Put a voltage source with zero volt and AC=1 between the + opamp input and R20.  The loop plot is the voltage at R20 divided by the voltage at the + input.