I think the thing to remember is that Dodge flows from the fiction. Usually casting a spell at point-blank range probably doesn't require a Dodge. But if the fiction says there's some danger you're facing along the way to the move, then it applies.
Another way to think about it is: does the character have to deal with the danger to make the move they want? If their just casting a spell at someone nearby? Probably not. On the other hand, if they're casting a spell despite being swarmed by stingflies? That might require a Dodge first.
But of course there are judgement calls involved, like with all moves, since we have to interprete the fiction. If we disagree online: not a big deal. If someone disagrees while you play, take a second, talk it over like adults, figure out what's going on, and work it out.
The classic example goes something like this (a variation of something that's in the text): You're playing the wizard and you say "Damn, Kither's in trouble with that orge, I'm going to cast Invisibility to try and get out to call in reinforcements. I start pulling the arcane threads to weave the spell into place." I'm the GM, and I say "Sounds like you'll have to Dodge the swarm of stingflies first, they're all over you." That isn't what you thought, so you say "Wait, what? I'm just casting my spell."
At this point, it sounds like we didn't communicate the fiction well. You were imagining this swarm as a few big bugs bothering you, I imagined it like a swarm of bees, distracting you from anything else. Since it's something outside of your character, I have the final say, but I should take what you think into account. The only outcome that doesn't work is when I still say the swarm is in your face, all over you, but you only roll to cast a spell: then there's something in the fiction we're ignoring.