The thing is, for me, anything I do while you're attacking is going to be meant to interrupt it. If you're shooting at me, and I move, it may not be an interrupt, but if I can get to you before you shoot, then I'm definitely gonna do that. In your example, it seems he's limited to just defending. What if he has a way to get to you before you pull of the shot?
Ex: Ian goes to shoot, pulling his gun and aiming at whatshiface, but whatshisface presses the detonator for his previously laid bomb at Ian's feet.
Or for a better example, my fight with Fallen, she went to shoot at me - but with my gun already aimed, by the time she did, I'd fired - so it would have interrupted her, or she'd have to take the shot to the chest, or keep it moving.
technically, that would be an interrupt, completely logical and all.
I don't mind snark, it doesn't bother me.
xD. But I mean, it's up to you. People are free to choose their own rules and all, I'm just used to interrupts(and prior to that, and I fought without them)