I think the biggest factor for contrast is the orchestration itself. This is not so heavily relying on the sections but more the timbre the individual instruments have. If you feel your melody written for low flute isn't cutting through you might want to change your supplying oboe in the same range, as well as letting the violins not play in the low range. If you're sure the orchestration works, and it's only the mix hindering from being clear, cut the unwanted low frequencies on the higher instruments, it helps a bit to take away muddiness. Shape the other instruments with EQ too in their dominant frequencies and you'll get a clearer image. Don't drown everything in reverb, less is often more. Setup two or three sections for front, middle, back and apply a different wet/dry ratio for reverb for each of them (or work with special impulses for that if you have those) to create depth.
Maybe you can post a little example with the specific lines in question and we can help you better this way?
PolarBear
Maybe you can post a little example with the specific lines in question and we can help you better this way?
PolarBear