[TowerTalk] Stacking 40m yagi's ??

[Jim Thomson]

A buddy is going to install a M2 40m yagi  [4-el]  at 180'... and a 2nd identical 40m yagi... at 89'. 

The question is.. whether a  upper /lower/BIP/BOP  switch should be used... or just a BIP/BOP ?? 

I don't have eznec... so bumbled my way through the maths... and it looks to me that  just a BIP /BOP switch is 
all that is really required.

When this same array was up b4... it was at 161' for the top 40m yagi.. and 90'  for the lower yagi.  At that time,
an AS  stackmatch box was used.. and the 3 x available configs were  top/bottom/BIP   [ NO BOP]    For domestic usa 
contacts, the BIP always outdid the  lower ant by itself... which baffles me. [ hundreds of tests run]
 The BIP  always out performed the Upper by itself  for all offshore dx contacts.   The BIP mode also was the loudest in W6 land..
a mere  800-1200 miles away ! 

Later on the AS box was removed... and replaced with a hb  LC box. ..[ npo doorknobs at left side.. and a series tubing coil, 50 ohms in
and 25 ohms out]   At that point it was BIP only... and it worked very well. 

This time around.. with the new  180'/89' config.... he is thinking of re-configuring the LC box.. and adding ONE vac relay..and
one 1/2 wave of coax  to enable  BOP operation.   [so it becomes BIP/BOP].     I'm convinced ...[on paper] that  BIP will outperform
the top ant alone.. and that  BOP  will outperform the  lower ant alone.    

Another thought is to build a u/l/bip/bop box... but to enable  top/bottom/BIP/BOP  will require  5 x vac relays,
and although doable... IMO... I think it's a waste of time.  Station is located in the pacific northwest. 

If I have it anywhere correct... I believe  the angle is slightly lower on the top ant by itself [11 deg]  VS the BIP Mode...[12 deg].. and even then 
the BIP mode will have higher peak gain.. and cover a wider range of 'lowish angles'.   

Somebody must have gone through this b4... are we close to reality here ?   Does anybody else  [on the west coast] have any experience with this? 

Tnx........ Jim   VE7RF