I understand why you would make a topic like this because you would have the following question.
What exactly is a complete FRS for yamato?
Remember he didn't know about the damage that it could give him to his hand because it was only after naruto went to tsunade that he and kakashi found out that naruto shouldn't use that jutsu again.
Also Yamato didn't see the improved FRS yet because he was out on a mission when naruto was fighting pain so yeah.
but think about this, where would naruto get the idea that he can throw FRS?
That's probably what yamato told him that he would be able to throw the FRS and expand at will by controlling with wind power but since kakashi needed backup with kakazu they had to pospone their training only to find that Naruto can't use the FRS again so they stopped the training.
He was just continuing what yamato was telling him to do by himself.
^ but there is no way to confirm this, it's only my logic and follow up with events
No one here or any where will be able to tell for sure whether Yamato/kakashi's 100% version FRS is what naruto used against pain. Both yamato and kakashi didn't see the throwing FRS so they don't know about it yet. Probably in the near future, we will be confirmed by yamato or kakashi that naruto's throwing FRS was the full version
As to can FRS still improve?
yes, from what it is now, I think it can be improved