This will not magically be overcome by constructive interference - each beam will still lose a significant amount of power as function of distance.

Well, yes, and no.

Each beam does "lose" energy compared to the theoretical amount it'd have without interference.

But the power you can transmit into any area inside the cells coverage is nearly constant, and you do not need to put that all extra energy your beans are "losing" into the transmiters, just a tiny part of it (due to errors, delays, object interference, etc).