I noticed that the article says to store the propane cylinders standing and then shows the forklift type racked on their side.
It then mentions that you want the pressure relief valve above the liquid level so you don't spray freezing cold liquid propane out of it if it pops.
What it fails to point out is that the small barbecue type bottles combine the relief valve with the fuel valve, so they have to be stored upright to get the valve away from the liquid fuel.