I can reach into my bag of tricks and postulate that there are different classes of navigational deflector systems. Perhaps there is a low power system that works well enough for certain classes of maneuvers that doesn't require a dish?
Or what if standard navigational deflectors (note plural) require no main dish and all maneuvers are available to the ship?
Ships with a giant sensor
dish would have a deflector built into it to help "tunnel a sensor path" for better long range resolution. The side benefit is that you get an additional multi-purpose deflector for pushing moons out of the way
That would mean that the heavy cruiser connie can just plain do more, such as:
The Paradise Syndrome
uses a deflector beam from the Enterprise.
IIRC, the original effects didn't show where the beam came out of, but the remastered effects have it coming out of the dish.
remastered FX: http://tos.trekcore.com/hd/albums/3x...romehd0510.jpg
Hmm. The beam doesn't appear to be coming from the dish (or at least not from the center of it). The beam looks like it is originating from the port side from a point on the engineering hull.