Yes, I spent a day doing the same thing as you. I tried to do the same thing with the F-4E as I did with the export viewport for other aircraft, but yes, the results were pretty frustrating. The radar and radar warning screens took up half the display and I had no idea how to adjust them.
Has anyone contacted the HeatBlur developers? I don't know if this is a bug or if they don't allow users to edit it this way. But the F-14B doesn't have this problem, and every viewport of it works fine.