Looking at that chart with the data laid out like it was gave me a brainflash, and I think I've finally figured out the penetration model:
NOTE: The following is my own deductions, it is not endorsed in anyway by SPCAMO, or the programmers!!!!
At a Gun's maximum range it will achieve only 33% of it's penetration.
At half of it's maximum range, it will achieve 66% penetration.
At a quarter of it's maximum range, it will achieve 82-83% penetration.
The variance in values between shots is the code that attempts to simulate real life in the game; e.g. simulating "lucky shots" that hit the tank in just the right spot to cause massive damage.
I did some tests to confirm my hypothesis before embarking on a statistical determination of the in between points; and have produced a spreadsheet that automatically adjusts itself to weapon range/penetration values; making developing guns for MBT/WW2 easy.
