This screen shows the different copper areas which are available for simulation.  Only the largest copper area is actually available on the Build It board which can be purchased in the Build It section of WEBENCH.
 

B. Click on a radio button to select a different copper area for simulation.  Click "Change Copper Area" to exit this screen. Return to WebTHERM - Setting up help page

A. "Click here to simulate all the available copper areas" will launch a batch of simulations.  This is the quickest way to see the effects of different copper areas.  Submit Multiple Simulations help page