Multiple Targets Limitations?

Okay, sorry, this has probably been asked and answered before but searching hasn't really gotten me anywhere on this question. A lot of abilities affect "multiple targets" but I can't find any clarification on what the scope of multiple targets can be affected. If a character is in a battle scene with like 10 minions, can an ability that hits "multiple targets" pretty much always target all of them? If a villain is using some Hinder ability that hits multiple targets, is it going to hit all the heroes on the scene? Like I could understand justifying if your heroes/enemies are discreetly split up by the environment (ie some heroes are engaging a villain on a rooftop while other heroes are fighting with minions on the streets below) the "multiple targets" would only hit targets in your perscribed area, but is it otherwise just whatever is in the scene at the time?

If your scene has multiple locations they are limited to what's in their current location.  Otherwise, it's up to the discretion of the GM and what the player can convince the GM they should be able to hit based off the power and quality used.  

Thanks, that's basically how I'd been calling it when it came up in my starter set games, but the D&D player in me wanted to make sure there wasn't a more concrete rule on it. Can't look at an AoE power like that and not see cones and lines and 20 ft spheres I guess, lol

I totally understand 

Keep in mind that, depending on the narrative behind the AOE attack, hitting all foes in one area might neccesitate hitting one or more allies in the attack as well.