Rates Are Higher Than Rack Rates On UPS.com

When I rate the following shipment on UPS.com I get a Ground rate of $10.90. When I rate and process the exact same shipment in ShipRush I get a Ground rate of $16.53. Why would rack UPS.com rates be cheaper than account specific rates using ShpRush? I did notice that ShipRush is saying this ship to address is residential, which is incorrect. This ship to is a business, and it rates that way on UPS.com. Even if you remove the residential fee of $3.40, the rate using ShipRush is still $2.23 higher versus UPS.com rack rates.

Ship From:
Davenport, IA 52806

Ship To:
1006 N HIGH ST
PORT BYRON, IL 61275

Weight - 1 pound
Dimenstions - 8x6x4

Thanks,
Chris