Why does one of my products have a much higher % fee than another?

I’ve been selling my own products via FBA for a while. I have two similar products but only today I noticed that one of them has a much higher fee than the other, and I don’t understand why. One of them is slightly heavier than the other, but it is the referral fee that is much higher, not the FBA fee, so that shouldn’t matter. Here’s the basic numbers:

Product A:

• Price $99.90
• Referral fee $7.99 (7.9% of revenue)
• FBA fee $3.96

Product B:

• Price $119.90
• Referral fee $17.99 (15% of revenue)
• FBA fee $4.75

So basically even though product B is $20 more expensive, I only earn $10 more from it, and since the production and shipping cost is near $10 anyway, I end up not making more at all.

What gives?