I've used some computer modeling to help prove out these designs before building them for testing. I've found the computer modeling to be fairly accurate and a great way to get me in the ball park. This computer modeling uses the NEC2 calculation engine which simulates the currents and voltages flowing through the wires. I use both EZNEC and 4NEC2 for modeling, 4NEC2 is a program that is very powerful and can be downloaded and used for free. The plots on this page are the result of computer modeling and the predicted gain curves and reception patterns.
These plots are a good representation of how different whisker and reflector configurations will change the reception patterns. The 10" x 9 1/2" and 9" x 8 1/2" patterns are similar just the curves are shifted higher or lower.
Click on the plots for a larger View