Armor Penetration
 

I've noticed that the Armor Penetration values at 5K, 15K, and 25K yards in War Plan Pacific (WPP) are roughly half of what they were in reality. As an example, penetration by the American 16"/50 Mark 7 guns (Iowa class battleships) was estimated to be:

29.39" @ 5K yards
23.05" @ 15K yards
17.36" @ 25K yards
(http://www.navweaps.com/Weapons/WNUS_16-50_mk7.htm)

yet WPP gives these as 14", 12", and 11", respectively.

Why is this?

Best regards,
-JPP