I'm animating a project in Cinema 4D and bringing the camera and 3d nulls over.
While Horizon does a great job of tracking tilt and panning, it's not really giving me the sense of space I want.
Take a look at this test footage. It seems the 3D test object is glued to the Horizon back wall, not floating inside a huge 3D sky which is how it should look.
Any suggestions on how to fix?
I'm not sure what you are getting at. Apparently your camera is rather far away and has a very long focal length, so it naturally looks "flat" since there is very little angular change. You't have to be much further in to see any meaning ful spinning of the BG. also be aware, that if your sky image is not very high-res, it may simply lack the detail to give an impression of motion because the same pixels have to be sampled again and again....