Featured arena iso?

Psychavi

Since the basic 4* says that duplicates only award +1 level and no additional prizes, that leads me to assume that dupes on the featured arena get additional rewards i.e. +20 and iso. I've also heard creaters like bg say that to get iso you should grind arena. But when I pick up 4* featured, I don't get any iso! Any ideas? Were they talking about 5/6 star? Is this only an issue for me? Is this how they're supposed to work? Any input is greatly appreciated.