37mm SA-18 couldn't be all that rubbish, if Polish armoured cars wz.29 recorded several destroyed armoured cars and light tanks, including Pz-I with 13mm armour (
http://derela.republika.pl/wz29.htm ). Most probably they had standard AP shots, and I doubt, if all cases were point-blank.
I've just read a Polish source, that steel 37mm bullet pierced 15 mm of cast iron at 1000 m (which is of course not armour, though). All in all, I feel, that range 4 should be increased a bit, maybe doubled.