I feel like these Ship Manager options are cursed so I'm asking here and not elsewhere.

I noticed picking "FedEx Box" is sometimes cheaper than keying in the same box dimensions by hand. Why exactly does this happen? I heard somewhere it's an incentive to help improve sorting. Do those boxes get preferential DIM factors or is it caused by rounding?

For my example I'll ship a 1-2LB FedEx® Extra Large Box (X1: Cube-shaped) across the entire US. You probably wouldn't use such a big box for 2LB but it makes it obvious. The dimensions are 11-7/8'' x 10-13/16'' x 11-1/16'' (30.16 cm x 27.46 cm x 28.10 cm).

2Day "FedEx Box": $16.29

2Day Rounding down to 11x10x11 (NOT allowed): $24.20

2Day Rounding up to 12x11x12 (correct way): $26.50

That's a $10 difference to ship exactly the same thing. It's something I check for now because it's occasionally cheaper to use a free FedEx box that's slightly bigger than to grab a box I own that's the right size.

Does FedEx even check if something is their own packaging? What would happen if you shipped a different box with similar dimensions and billed it as a FedEx Box? Or a Pak?

Also, why do Express Saver rates disappear if I select FedEx Box? I can get a rate for it if I use Your Packaging or FedEx Pak. It's like they don't consider Express Saver an express option.

P.S Is there any tangible benefit to checking "This is a residential address" on Express shipments since they don't get weekend delivery anyways? I notice if you miss it the residential surcharge is tacked onto your invoice with no penalty rates.

I heard recently that you can use your own box for Fedex One rate? What has been peoples experience with this? There is a chart somewhere out there that showed cubic inches and then what size it corresponded to. What was interesting is it looked like by using your own box you save money, or can use a larger box than the express boxes...