you need 6-10 letters

And I notice that you don't have any letter from US government. Usually, you'll need at least 2-3 letters from national labs or centers which represents US government.
The basic rule is to have your source of letter diversified as much as you can. For example, you can have 1-2 letters each from A, B, C university, and 1 from other countries (or 2 from 2 countries), and 2-3 from government.