I don't know what kind of hull you run or the length of it but this is what works for me. Both my 18' flats [Hondo & Howard] have the prop within 3/16" from the strut. I like to have the strut support the shaft and prop as much as possible rather than having most of the support on the shaft alone. Both boats take a nice set with no porposing at all with the plate in any position. Perhaps you need to extend and/or re-adjust the cav. plate.