> "move the burgers to the periphery of the barbecue"
That would be really formal over here too, the kind of wording that I'd expect in a grilling manual explaining how to use it, but not at a barbecue.
I can relate because sometimes I find myself speaking like that when talking to english counterparts, but mostly because when I'm "translating" my thoughts into sentences I have to choose between a group of words of similar meaning, and due to my inexperience, I often choose a less "popular" one.
EDIT:
After reflecting on this a bit more I also believe I often sound formal when speaking english because it's easier to use more/fancier words for the sake of not being misunderstood than it's to come up with a short, direct sentence that transmits my message in a clear way.
It's like adding redundancy to the message for reducing the risk of transmitting unintentional errors ;)