We ship from the factory directly to Amazon and into the UK.
We have to take a guess at what will sell in each area. It is deadly if we then end up trying to move goods from us to Amazon or Vice Versa. Also there are occasions where there is a limit to the amount available to us so we are forced to go one or the other. In general, Amazon gets priority on USA layout models that we think will sell fast. Anything else comes to UK as we can afford to sit on it here if we have to.
There are other factors sometimes but I think that is the most important.