I don't think anything beyond personal experiences\preferences indicate that dry-hopping cold vs. warm tends to more grassiness. I've done both (though not as controlled experiments), and have never experienced 'grassiness' as I understand the descriptor. Of course, I've not dry-hopped with 7oz. either! Awesome.
I have noticed an improved hop aroma by clarifying my beer before adding dry hops to the keg, which is all done cold, btw. For my current IPA in primary, I'm going to split my dry-hop charge in half, dry hop 1-week with half, then another week with the other half. Even with the same total amount of hops, is supposed to bump the fresh hop flavors even more than a single, larger charge. You might give that a try with the amount you're using and dry hop a bit in the keg.