Thanks to Mark Nankivil and Larry McCarley, I have a little more insight into the difference between the large and small radomes on the F4H. This is an overlay of McDonnell drawings of the forward fuselage:
You'll note that the ramp extends farther forward on the F4H with the bigger radome. That is one of the differences in the ramp between the F-4A and the F-4B. The change resulted in a modification to the aft edge of the lowest kick-in step and the lower access panel.
One of these days, I plan to reorganize and combine all the posts that I've done on the early Phantom IIs. In the meantime, I think this is a comprehensive list of them: