I think my contractor advised us that it's not possible to hang upper cabinets without gaps running vertically between the different depth cabinets. I say "I think" because this is coming second hand to me...I'll talk to him directly tomorrow. He advised using scribe, but it'll be a lot of scribe running horizontal and vertical. Is there another option I need to ask about? My old cabinets were hung in a similar configuration, and there was no gap.