Backspace for front wheels... Only 4 inches..

For front rims that are only 4 inches wide, the spider is gonna be pretty close to the center.A 4" rim will physically be 5" tall when you lay it on the floor. So with the spider in the center the BS will be 2.5". IDK, but I doubt you can move that spider more than 3/4", in either direction. That would make the bs range from 1.75 to 3.25 , and all will allow the front wheel to be inside the fenders . And all will spin freely on the spindle with no part of the rim or tire touching any other suspension part during suspension movement.
Whether or not the spider will clear your calipers I cannot say, but that is not a BS issue.
So then I ask; what would the backspace matter.

IDK, so I'm asking