Thought this online article was interesting in that it definitely states concierge is a 100% gratuity based position, and it sets forth the minimum suggested tip amounts. I probably have missed it, but I thought the consensus on this board seemed to be that no one knows what to do with concierge tipping. I should say, I have no idea where the article sourced it's information but thought it was interesting enough to share.
https://sites.google.com/site/disneycruisinggroup/cruise-info/concierge
https://sites.google.com/site/disneycruisinggroup/cruise-info/concierge