Yeah, armour in the game spawns with different values for regen penalty, or even without one which means that the coloured graphic near the sigma value in unaltered. That coloured graphic is like your "over 100%/below 100%" indicator, which means that you can control how the regen penalty on the armour is affecting your CAs. Armor Lore will always improve the regen penalty, I.e. make CAs regenerate faster, and to me it's pretty much a 100% needed skill on every possible build no matter how you play. It improves both your armour values and you regen penalty so it's a win win. I don't know how the exact cumulative formula works, but basically all values within the same modifier in the game are cumulative (more or less), so more is always more and less is always less.