In my experience, I tend to sit my SKJP Monterey a click high -- those clicks are close enough together it provides a great fit and still supports their head as it should. But, my kids who are on the last click or two don't necessarily need it a click up, as they're older/broader, and I have used it for one kid eeking out the last click and quite a few on the second-to-last click. So, since the click up is to provide better shoulder belt positioning, but by the time someone gets tall enough to need the top click they will probably be skeletally built differently and not need that click up, then my guess would be no. But I've never tried it so I don't know for sure.
That answer is assuming I understood your question correctly -- which is that most kids in SKJP need the headrest up an extra click to provide shoulder belt positioning, but the Diono the headrest can be "at" shoulders -- so they get an extra click in Diono -- is that right? (Excuse the bad run-on, lol!)