@ashmaan As GS says suggests, there are few, if any, spots for FA internationals in 11th grade at most schools. The kids we normally see transfer into boarding school junior year are local day students, or athletes, or students of families that are already connected to the school, or the odd transfer from another boarding school.
Junior year is a challenging one, and the schools you list above are leery of having a student from abroad tackle the twin challenges of acclimating to boarding school and handling the rigors of junior year curriculum.
Hopefully UWC works out, but I implore you not to put too much stock in a favorable outcome from the schools you listed. It is challenging as an international, incoming junior requiring full financial aid.