Usually in United States, three letters of recommendation are required by graduate schools but some applicants might ask more than more than three professors (say five) for letters. In this situation, there might be an issue of choosing whose-letter-to-which-school.
I wonder whether it is appropriate to ask each referee at which schools or departments they are relatively more well-known (having connections or interactions with professors in there) so that their letters are more powerful in there.
If it is not appropriate to do so, are there any efficient ways for students to determine to which schools should they send a certain professor's letter?
I am a little awkward with my grammar in this question (including the title). Please feel free to edit my question if you are a native speaker of English. Thank you very much!