I don't think it's an exact science either like, Aarons for example may as well be fucking Mexican. Dummett despite his lack of ability has the right attitude, I'd stick him in the centre until we get a proper partner for Mbemba. Colback doesn't, he's a little licky arse you can tell.
Santon was Italian but he took to the place really well and seemed to just get it, that's hard to identify abroad though, where as with someone like Austin you're relatively certain he'll fit. He knows the league, he has the right attitude, he can score goals, it's an obvious choice.