My gauge sits pretty much at 0 almost all the time when I'm driving around normally. Only time it would go up is under hard acceleration or slippery conditions. As soon as it's disabled, rear wheels spin. So my system works, maybe not as lively as a new one (haven't flushed/bled it), but it still works after 20 years. I don't see any reason it should be sitting above 0 during as it's not meant to be transferring (as stated).
If your gauge is above 0 all the time, you have problems, unless you're thrashing it literally all the time. Pretty simple and obvious.
Note that your ATTESSA is being worn out a lot quicker, they're not designed to run all the time. Direct experience, my system randomly craps out now (warning lights, hissing from transmission, system disabled, have to power cycle the car, needs a bleed at the very least). Before I put mismatched tyres on, it worked fine with no issues.