"The Preposition is often separated from the Relative which it governs, and joined to the Verb at the end of the Sentence, or of some member of it: as, " Horace is an author, whom I am much delighted with." " The world is too well bred to shock authors with a truth, which generally their booksellers are the first that inform them of [2]." This is an idiom, which our language is strongly inclined to: it prevails in common conversation, and suits very well with the familiar style in writing: but the placing of the Preposition before the Relative is more graceful, as well as more perspicuous."
- Bp Robert Lowth, A short introduction to English grammar

so that's the key: be more perspicuous in your usage!!