The only explanation of Naval Gunnery Algorithm, I recall, was mention by JWE, that at certain ranges hit is against deck armor, because of ballistic trajectory. Otherwise we can only guess.
I would be very careful in comparing penetration values for different countries, unless tests were made by the same facility. Different countries used different methods during testing, and this weird 10940 yards for Japan clearly indicates, that those are Japanese values for 10km. I read something, about US Naval tests long ago, and I'm sure they used completely different method, that ground forces. But for comparison:
- US ground forces used low grade RHA as targets, and penetration was described as "at least half of fragments on inside part of target"
- Germany used combat grade RHA (even hardened sometimes), and penetration was defined as "at least half of projectiles go through entirely"
So, US values would be quite optimistic in comparison to German ones. And remember, that "penetration" means that at least 50% projectiles will penetrate, not 100%.