Those vocals are "centered" simply by panning the vocal right down the middle.
But I suspect you might be talking about something different, and that is the solidity/presence of those vocals. For that the main answers are a combination of an excellent voice and vocal control (we are talking about Sade, after all ) and a light-to-moderate degree of compression on the vocal to help give it a consistent average amplitude.
BTW, I don't believe you are supposed to be putting someone else's commercial copyrighted material up on tindeck. Unless you are Sade or a legal representative of her label, you might be well advised to remove that file before they remove it for you.