[PlasmaKrab]

As you said, off-map range values are abstractions where the only rule is that e.g. 211 is higher than 210. IIRC, in the old games (maybe still in WinSPWW2?) the rule of thumb was that 1 range point equals 1 km over 10km (base value for offmap). I don't know what the current official rule for this is.