Err ... I'm not sure if I really understand the question, but I'll try to answer it anyway. :-)
With "ordinary" panning, you are more or less restriced to "left/right" and "more reverb/less reverb". As MIR offers individual impulse reponses for almost every spot on a stage, we are able to think in much more meaningful terms of "nice position for violins", "nice position for a flute". So if this is what you are asking for, then the answer is: Yes the width of an VI should be treated like on a real stage - as long as you think it sounds nice, of course, because nothing hinders you from doing it in a way that nobody dared to try on the actual stage.
HTH,
/Dietz - Vienna Symphonic Library