Amazon KDP Authors have trouble making the money they seem to be promised as well: even though my novel is available for sale through every Amazon.com website,

Amazon KDP Authors have trouble making the money they seem to be promised as well: even though my novel is available for sale through every Amazon.com website, and even though I'm supposed to receive a 70% (minus "delivery fees") royalty on sales in every market, I routinely have 15-20% of my sales in the US store get marked down to a 30% royalty. The explanation appears to be that these are sales from outside the US made on the Amazon.com website, but I fail to understand why that should affect my royalty rates. So Amazon's strange compartmentalization is at fault again. The net effect is that my actual royalty rate drops to about 64% of the sale price. This isn't a huge drop, but it certainly feels sneaky especially when apps sold through Apple net me the full 70% I'm promised every time.