Ideally you should use one fret per finger because it makes best economy of movement.
When talking about finger exercises... the numbers are the numbers of your fingers as well as their coordinating fret.
So if you were working on a pattern of 1324.... you would do first finger 1st fret, third finger 3rd fret, second finger 2nd fret, fourth finger 4th fret.
Or just apply it to higher frets that are more comfortable for you. Think of it like a game of pool, the shot is important but equally as important is where the ball lands so you can line up the next shot. Thats the idea with using all four fingers.