You just have to use your ears I’m afraid. I discovered early on that getting the gain set right really made a difference to the compressor, and you can crank it a hell of a lot more than you may expect. I tend to err on the side of caution and keep it around 11-12 o’clock because I tend to run an HX Effects in front of it, with some overdrive, so don’t want to mistake amp/cab distortion for something I actually want there at war volume.
Of you’ve got an Elf, I expect it has a similar gain structure to that as I can run that input gain very high before clipping, and feel I get similar results with the TE1200