I think he is asking if the pedal stack height for the Garmin pedals is the same as the Shimano SPD-SL pedals. Shimano 105, Ultegra and DA pedals all have different stack heights. 16.5 mm for 105 down to 13.7 for DA (current models). Garmin quote a stack height of 12.2 mm for their RS pedals, so if that's accurate then the saddle needs adjusting down by up to 4 mm depending on what SL pedal we are comparing against.