Yeah, most if it is simply learning what works and expanding on to that for flexibility/redundancy. For instance, I'd previously arrived at a known good starting point of ~1 meter spacing for a stereo pair of spaced omnis at this venue/mic-position years ago simply by adjusting things extensively while monitoring. This time I wanted to try a wider spacing in combination with the additional channels I'm running and purposefully decided on a 2 meter spacing for the L/R omni pair with a much shorter spacing to the Center mic. I did that partially from consulting Micheal Williams' MMAD charts for good 'critical-linking' of the recording segments between the three front mics (Left-Center playing nice with Center-Right) for my recording angle when played back as 3 or 5 channel material, but I also chose that configuration because I can can listen to just the Left and Center omnis as a stereo pair (or the Center & Right omnis). Those two mics are then at my known 1 meter spacing, with only a slight angular mis-alignment due to the center mic being ~7" forward of the Left one.
I haven't had a chance to listen extensively yet, but when I got home last night I did a quick multi-channel playback listen (no channel mixing) of just the omnis and played around with levels. Like your experience, I often end up using somewhat less of the center channel in support of the L/R pair to basically firm up the middle, but in this case with the additional base spacing and perhaps the Williams 'critical linking' array design, the entire front stage sounded solid and was best with all three front channels at the same playback gain.
