I'm going by what was in the article,

Plus, experts say cellphone location data, even at its most advanced, can only reliably track a smartphone within a few meters

This matches up with my findings when searching for more information.

Where do you get "18in - 12in" from?

I do plan to watch the movie, so maybe it will answer that and other questions for me, like where there's evidence of

The mules had to do this as evidence to their handlers and then to get paid. Around 10 dollars per ballot!