I finally finished my NEMA approved fire proof steel box to enclose both RPi3s and their power supplies, network switch and a 12volt power supply for the LNA once these emerge from the postal cloud.
The two RPis (T-KCLT3 & T-KCLT19) are stacked so you need to look closely to see the two FlightAware ProSticks.
WHilst this maneuver eliminated a 21 ft RG6 downfeed, it made virtually no difference to my range. However I am now in the position where I can experiment with antennas easily using short cables and with LNA power easily to hand. I just hope that the 100 degree F + temperature in my attic doesn't cook the electronics. Time will tell.