About 4db too low. The only adjustment on the FCP side would be your blackmagic card. Either a tweaker on the board/card like other audio gear, or a control panel in sys prefs, or an app that came with it to configure it, or even the gain control in FCP’s digitize tool (although most companies don’t take advantage of it and leave it ghosted out.) Could you be mixing everythiing to mono and have an out of phase cable cancelling things out.
Sure the bars are set to -12. But that’s probably for safety. They’d rather error on that end for sure. With loud tone, your dubs, etc. would come out lower because a dub house would have to lower the recording volume to match the high tone.. With low volume tone, your dubs would come out louder because the dub house would have to raise the volume.
-12 is just a number. That would only give you 12db of headroom until you have absolute clipping and distortion. Better hope any analog gear would also have the 12db of headroom. Better gear would have more headroom. Probably not a vhs deck.