Hard to follow your tests, with different parameters changes…
Red is the clipping warning, around - 12 db I think (MkI user), but with a sine wave you can go in the red without clipping. Easier to check clipping with a sine.
I’d say an healthy / safe signal would be just under - 12db.
@Open_Mike’s trick : you can check levels with the Noise Gate (Project > Control > Input). Increase Threshold to check input levels.