FCPX and Mid-Side recordings

Thanks for the added info.
I was wondering if this technique would add interesting sound capture in an interview context.
One camera moving around. One fixed camera and one or two people being interviewed,
In this case the recording environment is wide and fairly open.
The idea is to have the room sound blend in with sound FX that will be added according to how the story is told by the interviewies.
Just an idea I had.

Yeah sounds like an interesting idea. Might help putting foley in th context of the space too.

Then there is the time you want th dialogue and foley to b clearer and more punchy, in which case, less reverb is better, as well as tiny bit of loudness maximiasing. MaxxVolume or MV2 from Waves is a good tool for that. Simple and no fuss, especially MV2.

Be careful of using it on dialogue tracks that haven’t had any noise reduction used on them as it can bring up th background noise and unwanted ambience as well.

Ok. Thanks for the pointers.
I hope to plan and control the setting.
My main concern is the reverb and how much there will be in the room.

Recording in life locations is never ideal with sound, just as it is with controlling the lighting. Even though there are a small handful of tools out there that will remove excessive reverb, its not perfect. It seems to have quite a hard time removing slap back echoes, the type you get off a really tiny space. Trying to get the actors further away from the wall can help a little in this instance.

In capturing the reverb, it is what it is. If the director/yourself is shooting in a really ambient hall it's certainly going to be not so good for the sound. However if that's the space everyone is in then capturing an IR and "room tone" is going to be reasonably accurate.

Although in this instance, I would do as much as I can to try to remove as much of the reverb as I can, even gate it out. Then I would use the IR and the parameters within the IR reverb I am using and tailor the volume and the duration of the reverb, amoung other things, so that it's just enough to give a sense of the space and hide all the sound processing.

Thanks.
I plan on having some curtains nearby!
Since I will discover the speach level (volume) of the speakers and the location only on that day I have a plan B and C.
I might also shoot against a velvet black background which would help and I could then play a bit with the lights.

I've spent countless hours trying to get this right under FCPx and I'm wondering if something has broken in more recent versions. I'm pretty sure it used to work but I'm getting strange results now. Adjusting the mid volume mostly seems to pan the image rather than widening it. I'm running version 10.5 on MacOS 10.15.7. I finally tried it in Audacity and it works fine. I've tried the manual steps and the Voxengo plugin. Any suggestions?
Thanks!