Buck wrote:
"How critical would the matching of those beams have to be?"

Very.

Recall that a perfectl;y matched antenna delivers only 50% of its
received energy to its load. The other 50% is re-radiated. In the case
of back-to-back antennas, the load of one antenna is the other antenna.
The source resistance of one antenna is the antenna resistancce of the
other antenna.

If one antenna is shorted or open, 100% of the energy it receives is
re-radiated.

So if all antennas are in far-fields, and if all antenna connections are
lossless, and if all antennas are properly aligned, and if the match of
all antennas is perfect, overall system gain is the sum of the antenna
gains minus the path losses (both paths with a pair of antennas
back-to-back). Recall that the radiated signal loses 22 dB in the first
wavelength and 6 more dB exery time the distance doubles after that.

Best regards, Richard Harrison, KB5WZI