i’m probably just being stupid. i’ll go home and try listening to some stuff in both stereo and mono and i’m sure i’ll be like 
“why did i post that?”
i guess i just don’t understand the subtleties enough to apply it to my own music 
Trackid mentioned this and I say it again:
To check if you’d have mono compatibility issues, you don’t need anything like a phase scope or a vector scope.
You simply put a stereo expander on your master channel and turn it down to zero.
The result will be a mono sound and you’ll hear if any instruments are missing or too quiet.
actually i said that the method itself is correct but renoise stereo expander dont do it… you can try it… the instrument will be still there if you widen it 100% and put a stereo expander to zero…
but phase scope is still useful to get an image of stereo, of its widness and to see if it dont incline to the right or left…
For sure, I never said it’s useless. It just looks like a submarine’s…
Okay, about the expander:
Using one expander won’t give you the result. One expander doesn’t expand enough.
Use 4 or 5 expanders and the set the last one to zero. Then it’ll work.
Gilli… you still have to download a phasescope, do you?? 
No, that’s not why some sounds need more width. The reason a bassdrum shows a more vertical image is because the left and right channels are more similar. That’s the whole point of the vectorscope. When the two channels are exactly identical, the image is vertical, and the more different the two channels are, the more horizontal the image becomes. In the extreme case, the two channels are exactly out of phase and so the image shows a horizontal line.
But then that doesn’t take into account what the height of the vectorscope refers to, does it? 
Can you post a screenshot of the phase scope you’re using? I’m unable to download anything from the connection I’m using at the moment, but I’d like to see if there is any difference from the Ozone vectorscope and phase correlation meter I use while mastering.
Also, I’ve been searching for any helpful info on stereo imaging, but there really doesn’t seem to be a lot out there. Perhaps I’ll pick up something useful in the Waves S1 manual.
After reading the Waves S1 manual again, I came to realise how important a stereo pan control actually is, probably a big reason as to why amateur music typically sounds a lot more narrow than commercial releases.
A mono pan control colapses the stereo width when panning a stereo input either hard left or hard right, and so you need both a rotation and assymetry control when panning stereo sounds, as the S1 provides. A simply L-R balance control won’t give you that true sense of stereo panning.
Too bad I can’t post samples of both methods from this connection, but I think this is definitely something worth looking into in order to maintain a good sense of ambience in your mixes.
Exactly what I’ve been considering since the arrival of my monitors. That’s why I spent some time editing all my past tracks to adjust panning and width…
That’s why I have come to check out that large amount of samples…
Take the last thing I’m doing… I took this “airplane” sound and adjusted the width to make it sound “all around” the listener. Slided to 50% and the phaseimage was showing me a vertically stretched image… and the sound was still slightly “mono”. At 75% WIDTH the goddamn sound is playing perfectly around the listener and showing a perfectly round image in the scope 
About scopes, you are looking at the “flat” phasescope type like the one you continously see in the Waves S1 Manual… I am speaking instead of the “round” phasescope type… that’s what it looks like:
or like
and that’s why I speak about a “round” image… and flat vertical / horizontal lines…