[TowerTalk] How to create discrete phase shift in stack?

[Bill VanAlstyne W5WVO]

I have a StackMatch II (to be used on the 6M band) that I've modified to add a BOP capability by switching in a 1/2-wavelength segment of coax in the lower antenna's feedline when in the BOP position. This segment is permanently connected to the lower antenna's feedline through a T connector, but since it is 1/2 wavelength, it doesn't affect the perceived impedance of the lower antenna when it is open-circuited at the other end. This all checks out and works as expected.

However, because this stack is fairly low to the ground and the antennas are spaced only 1/2 wavelength apart (imposed design constraints), the HFTA model shows the main BOP lobe at too high a take-off angle to be very useful (around 40 degrees or so). I want to move this lobe down into the 12 to 20 degree range where I really need it, and I think I should be able to do this by changing the phase delay from 180 degrees to something less than that, maybe 90 degrees or so. Assuming my assumptions are in order, I have some questions:

1) What's the most practical way to accomplish a phase shift of other than 180 degrees? If I use coaxial delay segments, they would need to be relay-switched at both ends, not just one end as for the 1/2-wavelength case. Right? Is there a better way to do it?

2) How can I model the take-off angle created by different phase delays in this system over my actual terrain? HFTA only models a 180-degree delay. Can EZNEC do this? I have it, but have yet to set it up and get into it.

Bill / W5WVO