No math required, just common sense.

If you have a straight axle, you can put the spring perches anywhere up to the back of the hub, so you can minimize the amount of axle between the wheel and the perch.

If you have a drop axle, you can't put the perches in the bend area of the "drop" of the axle, you have to go inboard to the flat section of the axle to place the perch. Since most of the drop profile's I've seen are a ess-ish shape (two 45ish degree bends), instead of a right angle and a right angle, the distance becomes significant,

Not responsible for advice not taken...