[TowerTalk] Effect of Shunt fed tower

[Mark n2qt]

I have been trying to model the effects of a shunt fed tower in the middle of a proposed
4square.  I used n6lf's procedure as described at
http://www.antennasbyn6lf.com/2009/02/tower-resonance-measurements.html
What find is the indicated tower resonance tracks the shunt tuning. I.E. if the tuning is
set for 160 the indicated resonance is 160. If I select 80 (which I can tune with a variable
cap) the resonance tracks exactly.  If the shunt arm is disconnected these resonances
disappear and the resonance of the top loaded tower appears. I have only one shunt arm 
and select the appropriate matching network as required with vacuum relays. 

I presume therefore that the effective height of the tower for modeling purposes is 
set at 234/(Fres).  This way I can skip the tedious modeling of the tower, shunt arm and
the yagis that provide top loading.  It also implies I can set the effective height of the tower
at will, to avoid any undesired interactions if necessary.

Is this one of those things that's obvious to everyone but me? 

Mark. N2QT