Pierce Testing

99999 * 1.2 = 119998 for the second monster
99999 * 1.2 * 1.2 = 143998 for the third monster
99999 * 1.2 * 1.2 * 1.2 = 172798 for the fourth
99999 * 1.2 * 1.2 * 1.2 * 1.2 = 207357 for the fifth
99999 * 1.2 * 1.2 * 1.2 * 1.2 * 1.2 = 248829 for the last

Yep, that's the current theory, and it should be correct.

The idea stems from IA missing on wdef up'd bonefish.

Pretty much, the reason why pierce can break the cap is because the monster multiplier is applied after min/max correction, as is the IA multiplier.

So in the bonefish example:
Two bonefish have wdef up, the first takes 1 damage, the second takes 1*.9 which results in a miss.

In Pierce, the base damage could only be 99,999 max, then the 1.2^9monster-1) multiplier is tacked on.

Its pretty much confirmed by you not being able to break 249k *looks at your title*