[Sombre]

What lch is saying is that from the fact the head armour counts 20% of its prot value to the overall prot (the one displayed as a simple number of the unit stat screen), he suspects the chance of hitting the head is also 20%.

Legs/arm etc hits were removed from the game, so those don't come up in determining hit location, but are still used when calculating overall prot (which may be a bug) and since items can add prot to all locations (even the ones that can't be hit, ie not head or body) they can add more to the overall prot than they should seem to.