The only question I have, and this may simply be due to a failed Perception check on my part, is how do you figure out if two targets are near enough to one another to be hit by a blast, without those two targets being adjacent to one another? Would it simply be a case that one is written down as being nearby to the other, and thus is potentially hit?

The more I think about this the more I'm concerned it may end up being a lot of bookkeeping per fight to keep track of who's adjacent/nearby/etc. to whom.