[TowerTalk] Modelling Dilemma

[N4CW at aol.com]

Using EZNEC 2.0, I model a one-wavelength wire at 50 feet above real ground 
("normal"), and feed it at 50% from one end. I get a pattern that has nulls off 
the ends of the wire. If I change the feed point to 25% from that same end, 
the pattern has nulls off the sides ("normal" to the axis) of the wire.
I didn't realize changing where an element is fed would alter its radiation 
pattern. 
I am plotting the "total" field in an azimuthal plot. 
I'd appreciate someone explaining why this happens or pointing me to some 
readily-available reference material.
Thanks,
Bert, N4CW/1