Okay, simplified my point is that Khan made no prior mention or observation of the circle at any point, even after walking into the exact spot it was placed using his teleportation spell to get behind Metz.
Because he made literally no mention of it before, no charges would apply, as preps require you to clearly state you are preparing an action, and as I mentioned the circle was not mentioned once.
Metz obviously had to prep the circle, so it has one prep.
So, though his character will probably inherently have super reflexes and react to the rock forming at high speed around him, I believe this would fall under a 'surprise attack' in T1, where Khan has to accept his character was in a bad position due to his previous posts.
Also, Skallagrim has already stated a limitation on Khan's power, though this would be up to him to confirm, but it seems to state Khan's sword has no ability to magically effect the rock my character is manipulating 'just because its sorta magic.'
So, in my opinion this leaves Khan's character with very limited options to avoid being killed, and to my mind none that leave him completely unscathed by the rock shooting towards his character from all sides in the pillar. Technically speaking, Khan has already committed to his character believing the circle is negated, so if a ruling states it is not, his ability to then react to the rock would be dubious at best, and damage should have to be incurred.
The flip side is, if the circle is negated then Metz realistically cannot react to Khazna's super-speed blade assault, and Metz also dies. If the circle is ineffective for some other reason but Metz survives briefly, this battle is still over, I've already used every aspect of Metz arsenal to no discernible effect and Metz can neither see nor properly walk in the Arena, not to mention he's about to run out of mana.