Oh yeah so remember back in episode two when Akko leapt in front of Diana’s spell and got blasted with magic and then 2 minutes later she was 100% fine and we were all like???? how???
Well now we know why she wasn’t as affected by that blast as much as she should/could have been.
Because Chariot took away some of her magic. There was a lot missing. So the blast from Diana’s wand probably just filled it in a bit. If Akko had had all her magic properly and been hit by Diana’s spell on TOP of that, she’d probably experience some dangerous magical overflow of sorts.
BUT being that Chariot halved her magics, Diana’s blow was harmless to her because it just filled in some of the gap.