It is a tested and proven tactic in epidemiology.
It all makes perfect sense, but...
As far as bluetooth range goes, newer devices are capable of ranges in the order of 100 feet maybe more. <snip> Whether the range can be modulated or not I don't know but location can be triangulated with far more accuracy than range modulation.
But the app specifically ignores location, and under any circumstances, location is meaningless in this context, so, as I said, unless they can modulate the range of the Bluetooth on which the app runs the system will generate an enormous number of "false contacts," and those will, in turn, ultimately lead to an enormous number of people being told that they're at risk when they haven't even been near the person who's come down with symptoms.
And that will compromise the entire system.
That appears to be an aspect of the system that's curiously missing from the abstract.