If height is the correct term. Or you could say it's distance from the ground. I noticed this the other day when i decided to slightly alter a tech that that I use to transport resources to my selling bases. The tech has a deck of 6 Scotty's across the top of it's back end. They are not stacked, just two by two next to each other end to end forming one big one, and all facing up as normal. When I decided to move them 1 block higher the size of stacks they were carrying when full, dropped dramatically. Another block higher reduced their capacity even more and resulted in the two bottom rows of chunks were now stuck there and my base' collector deck could no longer retrieve them.