You want to go for the widest point on your ski and trim down from there - so typically your skis should be wider than the nose width of the ski. If you have really fat or rockered skis then you can trim a taper into the tip and tail, but you definitely want the skins close to the edges of the ski.
I haven't had experience with narrow skins, but I'd predict you will get decreased sidehilling and turning hold. You might not notice much of a difference going straight though.