ummmmmm...
Invserse Square law applies to the power surface density (e.g. watts per metre square) of signals emitted by
known point sources, usually RF radiation.
This has no bearing on the ablity of the a detector to perceive said signals, other than the amount of signal power available to a detector at a given distance from a given point source.
What comes into play at the detector is how much of the signal is captured, with respect to the background noise signal, and the sensitivity of the detector to the desired signal(s).
If the signal is indistiguishable from the background noise, the signal cannot the perceived.
This is what lets any radio communications operate over distance - the transmitter emits RF radiation, the receiver collects
some of the RF radiation and detects the signal. In the case of cellphones and other terrestial phone systems, this is then relayed either to another RF repeater or over fixed land lines.
As other have pointed out, even if prayer was subject to the inverse square law, unfortunately this makes no statement about the machanism by which the prayers are received (peceived?).
Please, let's not get into the wave-particle duality as well (Where's that can opener

)