A quick story about Channel Tools: I was working on some spoken stage audio recently, recorded with two condenser mics on opposite sides of a performance space. When using Channel Tools to narrow the stereo field, I noticed significant harsheness caused, most likely, by phase cancellation. Because if a sound from the left mic takes time to travel to the right mic, and some of that left channel is mixed straight into the right channel without the delay, phasing issues (and therefore harshness) may result.
I ended up using Izotope Ozone's stereo imager for the job, and the result sounded much, much cleaner. Maybe it's because Ozone can detect and compensate for such delays. Or maybe it's because I did most of the extreme centering on lower frequency bands, and just did a partial stereo field reduction on the upper bands.
The moral: if you have Ozone, I'd suggest using that instead.