[VHFcontesting] 6m Array Switching

[Ev Tupis]

Hello everyone,
I am assembling a 4-dipole multi-driven array (horizontal polarized, stacked up 
my tower).  At first, I was thinking about simply stacking them all 12' 
(5/8-wave) apart and feeding them with 3/4-wave 75-ohm harnesses and calling it 
quits.  However, my thoughts are now wandering and am interested in exploring 
the ability to select between:

Upper Two (50' & 38')
Lower Two (26' & 14')
All Four  (50', 38', 26' & 14')

with the desire to focus the elevation component of the array to take advantage 
of different DX conditions.  A couple of questions for those in-the-know...

Has anyone done this (array switching on 6m) with any degree of success?
  - How have you accomplished it?

What height does one use to calculate the takeoff angle of each combination?

"Let the tread begin" :)

Ev, W2EV