A lot of cellular is limited by LOS
If you don't have line of sight between your device and the tower's antenna (passing through trees is fine, but hills not so much) then increases in SNR via this method won't help you all that much, because you aren't being limited by too much noise but by too little signal.
In lower frequencies you can get one edge or two edge diffraction paths where there is no line of sight, but those are always kind of sketchy and depend a lot on time of day (i.e. localized heating of the atmosphere) and also position so they don't tend to maintain signal lock well with a moving (i.e. you in a car) target.
