Indirect Combat Spells/Grenades and Targeting, Question related to FAQ Options

[Speed Wraith]

The FAQ indicates that if you use ICSs or Grendades with the intent to catch a target in the blast radius then the target gets an opposed roll (rather than a success test), but how would this apply in a blind-fire situation? I can easily see my group running into a situation where they know for a fact that there are hostile targets they cannot see, such as some security guards taking cover around a corner. They may not know exactly how many guards are around the corner, or how close they are to the edge, but they like to blow things up so they decide to toss a grenade (or fireball) down to the end of the hall. In the case of grenades, I'm assuming the -6 modifier would apply for blind-fire, but would that also apply in the case of a spell?