This is obviously an old thread but I was having the same problem with ‘Narrow’ mixes that had almost no stereo imaging.
Please, don’t just tell me I’m a total newb, tard, amateurish moron, or can’t mix very well;. I already know all of that stuff, thank you 
This was never a problem with stereo imaging when using Nuendo, but in Cubase 7, noticed a total lack of panning in the mixes on which I inserted the Spacial Stereo Enhancer into the main stereo outputs.
I started the elimination process by panning one over head drum mic hard left. The sound was coming through headphones in both left and right channels and was thus indicated by Cubase 7’s Stereo output meters.
I Soloed the track and began turning off the few processors in use one by one. Panned hard left the audio i was still coming through left and right channels, equally.
When I turned off the Spatial Stereo Enhancer, the selected track which was panned hard left, audio then came only from the left channel in headphones and was showing only reaction from Cubase 7’s left meter indicator of the main Stereo Output.
Maybe ‘resetting’ the effect helped. Perhaps I had set it incorrectly; but I expect I used a standard preset. That may have been the problem; I just used the wrong preset.
In addition:
First, I had the Stereo Imaging effect after the Maximizer in the Stereo Ouputs insert chain, pre fader.
I moved the Stereo Imager to an insert point before the Maximizer and that produced a better stereo image. Adjusting the ‘Width’ to about 150 w Delay and Color turned off improved imaging more.
Engaging the ‘Delay’ and ‘Color’ section of the Stereo Imager immediately put everything in the middle again?
That’s what happened with the Spacial Enhancer Effect when used in the main stereo outputs for me.
I hope this helps you
Have a nice day