It's due to a pretty obnoxious set of edge cases: you do bomb damage in 5 point clusters. However, FAE bombs do 1.5x damage (got to fix the report) to units with armor that has a BAR < 10. To further complicate things, units may have patchwork armor, so just because one location has low BAR doesn't mean another location has the same BAR.
As an example, let's say you have a unit with crappy patchwork armor BAR 7 on the center torso and BAR 10 on the right torso. You're one hex away from a small bomb fuel-air explosion, so you take 10 damage. What do you do now? Do you multiply the damage by 1.5 even though the multiplier doesn't apply to the right torso? Do you multiply the individual 5-point clusters by 1.5 for locations that have BAR < 10? I went with the latter option. It may be a rules question, or may have already been answered, I'm not sure.