That's actually a much more logical place to PUT a ramscoop -- or at least some kind of gas intake for siphoning fuel from the atmosphere of gas giants -- since it's actually relatively close to both the main reactor (where that fuel is really consumed) and whatever hardware the ship might have for converting matter into antimatter prior to its consumption. For that matter, it also has much better forward clearance than the nacelles and is in a better place overall to BE a ramscoop than a deflector.Orange is the rough overall impression we get from the multicolored TOS ramscoops, too. Perhaps "ramscoop" and "deflector" are more or less the same thing - a vital path-sweeping device? Redshifted rather than blueshifted because of the suck-not-blow function?
Still, I doubt the dish actually has anything to do with "deflecting" at all. It's probably just a big radiotelescope for scanning ahead (like its real-world counterpart). If the ship has any sort of gas intake it's either attached to the base of the deflector or built into the nacelles for skimming atmo as the ship moves through it.