Installing Walthers 90 ft. Turntable on Foam Base

I want to use foam sheets over plywood for my layout base.

How deep should the foam be at the turntable location (i.e. how deep is the $40.00 Walthers turntable, excluding motors, etc.)? This dimension is not shown on any product literature.

Thanks in advance.

I looked at the photo of the turntable on Walthers' Web Site. It doesn't appear to be any deeper than 1½" OD at the very most.