Magnets need to line up?

I was looking at 6 string pickups for a project I wilil be doing. I foind that 6 string pickups come in a variety of sizes (for different string spacing?) So my question is: do the magnets on pickups need to line up perfectly with the strings, or will it be fine as long as the pickups is placed with the same amount extending beyond the highest and lowest strings? Do I need to shop around for a pup that perfectly fits my string spacing?