Quick question about MDR

[Pansesus]

Stream=line of projectiles coming from a single source, generally headed towards a single target(ie, like if someone blew a stream of Inferno particles at you while you had Chilling Armour on, you would counteract with a stream of Ice Bolts)

one of the streams doesn't get affected by MDR

So inferno spell contains more than one stream, and one of them is not affected by MDR, right? Now comes another question, how many streams are there in inferno / arctic blast, and why is this "specific" stream not affected by MDR. Just seems a little bit more confusing. Is there some good reference on this topic?

Thanks very much!