You can set up any way you like. Important is to have enough bio media to handle tank bio load. Do not put carbon in any. Using poly fiber will indeed catch finer debris particles, but will also make for more frequent canister openings. The fiber will need rinsing or replacing 2-3x more often than the mechanical sponges. If you are committed to using those filters long term, I would set one up as primary bio, the other as mechanical.