IB is on Touma's right hand. If his right hand is damaged, IB is being damaged. We literally see a few lines after that how it hurts Touma's hand, a feat only replicated by Gungnir and Limen Magna, IIRC.
A crack ran down the fingernail of his right index finger and red blood flowed out.
Even so, Kamijou did not give up.
"You've always, always wanted to be the heroes, right!? You wanted to become the kind of magicians you find in picture books and movies that risk their lives to save the girl, right!? Then this isn't anywhere near over!! It hasn't even begun!! Don't fall into despair just because the prologue dragged on a bit too long!!"
The magicians' voices were silenced.
Kamijou would not give up. What did he look like in the magicians' eyes?
"If you stretch out your hand, you can reach it! Just do it already, magicians!"
An odd cracking noise came from Kamijou's right pinky.
When he realized the finger was bent ― broken ― at an unnatural angle, the pillar of light attacked with tremendous force and finally knocked Kamijou's right hand away.
His hand was knocked a good ways back.
Cancelation speed is not a good answer to that when we've seen him stop much more powerful stuff without the hand being hurt at all, like Aqua's super mace drop or Fiamma's/Aiwass' attacks.
IB is inconsistent, which is why I think that currently it should not be scaled to the highest feats. If more feats make the higher ends more consistent it'll likely be upgraded, but for now, there's no reason to do so.