I have a 14 and I probably over obsessed over where to put the antenna. Due to the ability to choose between wheel or three point landings, only place that remains constant, in relation to the runway, is between the main wheels. On an RV-14, that just won't work.
I mapped the belly skin for the 120° cone that nothing can protrude into. For me, I had the comm antennas and the steps. The black tape lines show the areas that are not suitable for the GHA-14 mount due to the 120° requirements. There is an equal area, not marked, for the other, un-installed step.
In the end, mine is forward of the area recommended by Stein and it works great. I can't tell the difference between wheel landings and three point landings.