Chaos Thrust is Worthless!

[Rex]

There's nothing written specifically that you have to hit from behind for the combo to work. However, you should have known from Vorpal Thrust that it gets its combo effect when there's a rotating square thing around it. Thus, anytime you don't see it on Disembowel, it's not counted as combo so the logical thing to try would be try to get it hit from behind for maximum potency.

Impulse Drive: Delivers an attack with a potency of 100.
180 when delivered from behind target.