I don’t expect nothing in particular, as the two positions - the real one of my finger and the one of the pointer - are completely wrong: if I move, it moves too, but when I am in a corner it starts from the center and so on
That's very telling behavior and explains why the Dolphinbar wasn't recognized. The touchscreen is apparently being read in this case as a standard relative coordinates mouse. If it were being read as an absolute coordinates pointer device, the cursor would snap to wherever it was you touched at. Needless to say, this limitation combined with the wide area required to receive input really hinders precision.