My xpndr and ADS-B in antenna are installed about 8" fwd of the spar on each side. This is a -7A, so they are just under the MLG weldment, which protects them and their coax.
I think most tail draggers install them per dlloyd's recommendation. A friend installed his in the aft fuselage and they were broken off a number of times by dogs or people crawling under the plane. Ask me how I know
