I could be wrong (like my disclaimer? ) but I believe that the Trim Setting is to adjust how much deflection one gets at any particular control surface when it's trim lever is adjusted/moved, i.e., if the trim setting is too sensitive (moving too much), one can lessen the sensitivity. At least, that is how it is on the 7C and 9C. An easy way to tell is for goirish to enter that mode and try it. If the control surface does not move when adjusting the values, it is not acting like sub-trim.