here they say at least 1.5 but indeed i think that only applies to open space. The rest is just statistical bulk prevention and mostly (i think) prevention of friction from too many people per m² during times of high stress, someone already got a beating here for 'not following the rules' (and not from the cops) i myself have run into some strange people (and i usually am the strange one)
I think coughing or sneezing can reach 10-15 metres actually, is what i read once. Laws of physics might have changed and the info might not have been completely accurate. I dont know how many times a snot particle can bounce CDC gives no actual numbers ,

hoh, here it is : MIT apparently finds it can go up to 8 metres but the fat ones travel only 2 :)

flu survives 24 hours on metal, corona up to 72 i think

its purely damage mitigation, by no means a secure means and people who works as store clerks in foodstores (unless they are alone) cant hold that anyway. Its all just about reducing the numbers.

8 metres :p ... which would make life impossible unless you get everything delivered at home i guess