Out of curiosity, I brought up an EZNEC model of two stacked 5 element
beams from the ARRL Antenna Book, 20th Ed., model ARRL_5L15 95'.EZ. I
deleted half the elements to leave a single 5 element array, and lowered
it to 65 feet. I also changed the current source to a voltage source for
simplicity, and removed the wire loss (which EZNEC translates to NEC as a
bunch of loads) -- the wire loss makes a difference of only 0.05 dB.
Here's an NEC model of the 5 element array up 65':

CM 5L15 95'
CE
GW 1,11,-3.464585,-3.528538,19.812,-3.464585,3.528612,19.812,.008906
GW 2,11,-1.766258,-3.345701,19.812,-1.766258,3.3457,19.812,.0088644
GW 3,11,-.4925144,-3.283913,19.812,-.4925144,3.283913,19.812,.0089841
GW 4,11,1.120895,-2.98782,19.812,1.120895,2.98782,19.812,.0087506
GW 5,11,3.464584,-2.793987,19.812,3.464584,2.793987,19.812,.009137
GE 1
FR 0,1,0,0,21.2
GN 2,0,0,0,13.,.005
EX 0,2,6,0,1.414214,0.
RP 0,1,361,1000,80.,0.,0.,1.,0.
EN

Gain as-is is 14.11 dBi; with loss, 14.07 dBi. Zin = 21.51 - j22.26 ohms.
Takeoff angle is 10 degrees.

Seems to me this would be a lot easier to build and support than the
"Gaussian" model. And I'll bet you could make up the half dB gain
difference quite easily by adding a sixth element.

People with the 20th Edition of the Antenna Book can open the model, make
the same modifications I did, and run it with the EZNEC ARRL program
furnished with the Antenna Book, or any EZNEC program type except the
demo.

Anyone who's impressed with the gain figure of either antenna should model
a dipole at the same height for comparison.

Roy Lewallen, W7EL

A dipole at 85 ft shows a gain of 7.5 dBi, with a TOA of 11 degrees.
Using ARRL's program "YW" a 6 element Yagi at 85 ft has a gain
of 16.7 dBi on 14 MHz.

Running Roy's program, above, I get exactly the same results. The
F/B ratio is also excellent at 28 dB.

Frank