Even on a metal armor JHP suck hard. Believe me, if your ennemy have better than a leather jacket, take AP ammo.
I'm not sure about your formula Midnight, but what Drakonis said about results is true. You want to hurt an armored target with a Minigun, you hose him with AP, end of story. JHP is going to work too against stuff like Metal Armor mk2 without psycho, but in the end you're going to have AP being slightly more effective on this level and really making the difference against better protection. Since I don't think there's some voodoo magic going on it must be the fact that something's wrong about the formula or you're not taking something into account. I mean I've shot PLENTY of people with .223, 5mm JHP and 5mm AP with a top tier big gun (LSW, Avenger) and I will easily choose AP loaded Avenger for PvP any day of the week - it simply works against lightly armored targets and works best out of the three against guys in Metal and better.
If you want to make enemies, try to change something.
I think most JHP/AP guns are crossing over at the correct points now. The change a few months to 5mm AP was to get this cross over happening in the correct place ... as well as to nerf miniguns on CA+