No the magnetic field needs to fit the bass's string spacing. The wider string spacings at the bridge would need coils that have magnets over the strings. When the spacing at the bridge is 16.5 mm, this requires on magnet spacing on the pickup vs 19mm bridge spacing. Also the nut spacing plays into this as well for the neck pickup.
Duncan makes two different spacing's and sizes of 5 string jazz pickups that I will use as an example.
The first pickup is designed for more narrow spacing 5 string basses. These are listed as a 67-70mm total string width pickup. There would be 4 spaces inbetween that total spacing, which means they can be used with a bridge string spacing of 16.75-17.5 between strings (70 divided by 4).
Larger spacing pickup has been widened, because the magnetic field needs to extend further to cover the width of 70-74mm (up to 19mm between strings) total string spacing. Duncan say "Calibrated neck and bridge set. Comes in two popular string spacings: 67 mm neck with 70 mm bridge, and 70 mm neck with 74 mm bridge."
much like this 5 string 1/4 pounder pickup.
This pickup is a direct retrofit for Fender® Jazz V and many other popular 5-string basses. Will accommodate string spacings up to 3.10" (78.7mm) for bridge pickup and 3.00" (76.2mm) for neck pickup
This means it is the larger sized Jazz pickup made for string spacing up to 19mm at the bridge. That is a wide pickup.
When the pickup has a bar magnet, the only consideration you need to know is what EMG says. This is taken from their 4/5 string J Set pickup manual:
Both SJ and LJ Housings can work with both 4 and 5-string instruments, but you should check the width of your strings against the magnet dimensions above to make sure there is sufficient string coverage. A rule of thumb for any pickup is that the total magnet width should be the string width plus twice the distance the pickup is from the strings. So, If the pickup is 3/16” (5mm) from the strings, with a magnet width of 3.10“ (78mm) the maximum string width would be 2.72” (69mm). |
That is a great rule of thumb for a bar magnet pickup.
But for the pickup your choosing a SD Basslines soapbar for a 5 string; then
The maximum string length is close to 80mm. Essentially, that will work with any string spacing on a 5 string to 20mm at the bridge. No you don't need any other considerations than that. That pickup will work without changing any plans you already have in place.
Hope this helps explain string spacing and magnetic field a bit.