Place a shulker box at the height limit, 255 Y. Then, place one just below it. Now, make a platform to stand on at 253 Y, so your head is next to the top shulker box. Now, with an empty hand, shift-click both Shulker Boxes and compare what happens.

The height limit Shulker Box opens, while the 254 Y Shulker Box doesn't and just swings your hand.