Because I wasn't properly setting my gain levels in the first place.
The opportunity to sing and record vocals would happen so quickly that I'd just plug it in and make sure there wasn't any clipping. Today, coincidentally, I had a chance to sing but I spent about 30 mins checking input gain at the interface level
Sure, it's important to get the gain right but it's a 10 second job usually.
Set gain, perform at your loudest and closest, turn it down a touch if you clipped or up if it's ridiculously low, repeat.
There's no rule and specific advice varies but just make sure there's whatever you'd deem a comfortable amount of room between the extreme peaks and red lights.
In rarer circumstances it's possible to overload the microphone without clipping your converters or overloading the preamp.
Usually you'll know this is happening because your recording will be distorted but your gain will be at zero.
It's only ever happened to be with capacitor mics on snares and that kind of thing.
If you're in someone else's studio the rules are different. Soundcheck really really quietly then every time he's doing an actual take just suddenly get a shit load louder.
If your recorded levels are healthy and not clipping with the gain somewhere > 0 then that's about all you need to know, really.
Once you're in the box, boosting or attenuating a track is a different decision made by different criteria. That's mixing.
Apparently, line/instrmnt on the 2i2 doesn't do much, if anything, for a phantom powered mic. does that sound right?
Yeah.
Instrument/line controls govern anything plugged in to that channel via 1/4" connector rather than XLR.