ROFL
First, I know how penetration works in this game, and second, don't lie. I tested Bofors vs P4 dozens of times and every time the P4 has won with over half health. This is also assuming the battle is completely a 1v1 fight, no ISG's or shrecks. I have never ever played a game where a Bofors was ever a threat to Axis armor. Meanwhile, the Flak truck penetrates most Allied tanks consistently and half the time even wins the battle.
Perhaps you tried the OKW p4 which has more armour?... The ostheer one has 180 armour and it is a toss up which dies first.
Try it. All ranges.