[TowerTalk] Stacked KT34XA's vs The Competition?

[Brad Pioveson W9FX]

Greetings, TT'ians.  In a conversation held yesterday with a friend who's an 
avid contest op, the subject of stacked tri-banders came up.  My friend 
commented that he has a stack of three KT34XA's on a tower, one each at 
120', 80' and, 40', all connected using a StackMatch device and fed with 
low-loss line.  He mentioned that he's never been impressed with the 
performance of the stack vs his 5 ele monoband yagis for 20 and 15 located 
on an adjacent tower at 120' and 100', respectively.  "Only very rarely," he 
said, "will the stack - with the antennas taken singly or in any 
combination - display an advantage whatsoever when I compare signals with 
the 5 ele, long boom, homebrew, monoband yagis for 14 and 21 MHz.  The 
monobanders will, in nearly every case, outperform the stack."

That got me to thinking...  I don't recall seeing KT34XA's mentioned often 
in contest station writeups as the tri-bander-of-choice for stacking.  Are 
my recollections accurate, and, if so, why is that?  I do remember having 
heard, worked, and or read about other brands of antennas being used...but, 
not KT34's.  Is there a reason...does the KT34XA design and pattern 
(patterns, considering all three bands) not lend itself well to a stacked 
setup?  Or, should this stack work better than described?  I realize I 
haven't given any hard performance data, only the comments of the guy that 
built the array, uses it regularly, and is puzzled as to why it doesn't 
'work' better than it does.

If my friend's stack of KT34XA's is not performing as well as, say, an 
equivalent stack of TH6's, F12's, it also strikes me that now - during the 
solar cycle lull - would seem to be an excellent time to start on a long 
range plan to swap out the antennas with those that will make better use of 
his 120' support, Ring rotors, and associated hardware.

Thoughts, anyone?

73, Brad, W9FX