The ideal conditions are almost never achieved in ordinary ground communications, due to obstructions, reflections from buildings, and most importantly reflections from the ground out of phase. This fading can cancel up to all of the signal. So it is more important you define the path and all reflective surfaces and the intended use. Much gain can be obtained by aiming a narrow band expensive antenna and avoiding nulls. You have adequate signal power for 50m but unless you control all the paths emitted and reflected, you will have no control on the received signal integrity with the possibility of all the signal at some positions being totally lost. There are tricks to improving range such as lowest data rate, and better Lithium batteries, and more with antenna aperture shaping. You can expect performance as good as an average bluetooth modules. Don't expect 20 dB fading unless you know that 40 dB fading exists too and the lower the signal, the greater Ricean Fading.