I think you may be thinking too hard on this. I don’t think sales have any relation on what Amazon ships. I believe it depends on who orders first. After the first shipment from WAC is sold out, which Amazon more than likely orders a limited amount, then it takes a week or so for them to be...
I feel for you. I went the Amazon route for along time waiting up to a month and a half for the title. I did this so HTF would benefit from the order. I eventually witched to WAC to get it in release week.