That might be what does it. I don't remember if I initially did this in slow brawl or not.Here are my new results, can you confirm?
Late aerial:
2676 at 9%
9717 at 309%
KGR: 23.47
Base: 2464.77
Spike: (early aerial)
2931 at 12%
12907 at 312%
KGR: 33.253
Base: 2531.96
and for comparison purposes: Bair
bair:
2129 at 13%
12822 at 313%
KGR: 35.643
base: 1665.64
Although that makes sense, come to think of it. In slow brawl, your opponent travels slower. Maybe the mechanism the designers use to measure launch speed doesn't compensate for slow brawl. That's another thing that would need testing.