Antenna gain & link budget
We both agree your link budget analysis is wrong.
You forget that antenna factors only apply to far field! You can't have two antennas sitting &quot;right next to each other&quot; , i.e. closer than the Fraunhofer distance, which is \$2d^2/\lambda\$, with d being the dimension of the antenna defining the directivity of emission (typically, it's simply the largest dimension of your antenna). A 10 dBi antenna will be rather large, so that quadratic part really says &quot;can't claim 10 dBi gain and 'right next to each other' at the same time&quot;.