My kobra 2 didn't come with one of those gauges. I manually set the probe to 1.5mm higher than the nozzle with the nozzle JUST touching a sheet of paper on the print bed. My offset is dead on at -1.40mm now and the probe reads perfectly. Frankly I found them to start getting less than consistent approaching 2mm so I had to do a bunch of testing before I found the 1.5mm sweet spot.
If that gauge is accurate (5.5mm and 3.5mm tall) then yes, your sensor is slightly too far down.
Alternatively just compensate by setting a z offset for the entire print.