If recording group-vocals, we can hear and judge instantly for the required sound, through studio monitors.
Rather than recording in groups, I used to stack voices of different singers, who sang @ different place different setups. Especially during pandemic lockdown days, singing chorus was not very happening, so I used to do this.
Recently, I was doing the mix of such recorded song. And I felt the vocals slightly lacked clarity. I tried out with Eqs. It did help. But was not fully satisfied. In a second sitting for the mix, I thought to checkout the PHASE of the wave forms of the group vocals. And YES it was the culprit. Some tracks with same melodies had, their phase slightly mismatched (—in simple words– wave form of one rising while other is going down; you have to really zoom in the track to see this). And little-little in each track amounted to huge difference.
So how do you fix it?
Two ways
1, Invert the phase of one of the tracks, listen for the difference.
2, Move one of the tracks in time line to align the peak.
In any of these ways listen and take the judgment, not with visual of the wave form alone.
This PHASE issues comes in recording groups, multiple mic setups. Very drastic things happen in Low frequency range, if not careful with PHASE angle.