By the way, after using [Triple Stab] I confirmed it. It really turns out physical defense was ignored. However, there seems to be a requirement where the attacks pierce to the same depth as the middle attack.
Furthermore, the size of the hole naturally depends on the weapon used to make it: A hole left by a halberd is going to be larger than one left by an estoc due to the strength of the blow.
The ability that helped me the most was surprisingly [Vampiric Exploitation] that I got from the Seven-Colored Bat.