Assuming you are running something close to 14" of setback and assuming you have a sportmaster lower unit or a coned 200 case with low water pickup and assuming the lip on the pad has not been removed or reduced... Yes 1/2" to 1/4" below pad is generally a good place to start.Ended up going with a 20" mainly because it was the most affordable at the moment. As far as engine height adjustment, should my prop shaft be around 1/2 " below the pad?