Query on toriod -> ground capacitance

Subject:  Query on toriod -> ground capacitance
  Date:   Fri, 13 Jun 1997 01:36:23 +1000 (EST)
  From:   Rodney Graham Davies <Rodney.Davies-at-anu.edu.au>
    To:   tesla-at-pupman-dot-com

Hi all,

A friend of mine wanted to know this -

"Why does the capacitance to ground of a toroid increase when you bring
up higher ? This is an odd occurrence and is probably not linear."

My own theory is that raising the toroid is practically the same as 
increasing the spacing between to capacitor plates. Here, the plates are 
the ground plain and the toroid...I could be wrong...

Anyone care to elaborate?