In that case, that sounds like Amazon is charging you differently based on how other people are using their resources. In the times of surge pricing, I wouldn't

In that case, that sounds like Amazon is charging you differently based on how other people are using their resources. In the times of surge pricing, I wouldn't be surprised if they are doing that to make it so they make the same amount of profit, regardless of how much you are directly using, but depending on whether they are getting enough money from all tenants of a particular shared host. So if other people are paying less, they jack up your pricing to equalize things out so at the end of the day, their systems are still hitting their profit target.