How's this?
Range Category || % of hits on deck
============ || ============
long to very long range || 90%
long range || 80%
long to medium range || 65%
medium range || 50%
medium to short range || 35%
short range || 10%
Range Category || % of base damage inflicted
=========== || ===================
long to very long range || 80%
long range || 60%
long to medium range || 40%
medium range || 25%
medium to short range || 15%
short range || 5%
So a 38cm hit fired from long range at a ship with 10cm deck armor will strike the deck 80% of the time, and inflict 13 pts damage ((38 * 0.6) - 10) = 12.
.
One addition to Red Admiral's distribution of damage, to reflect the effects of large-caliber non-penetrating hits, we could say that 30% of non-pentrating hits on a main battery turret disables the turret, although it inflicts no actual hull damage points. This gives designs with numerous lighter guns a fighting chance. This would come into effect for guns 28cm and larger.