I can't get the math right on how high to install the hanging rail. Ikea instructions say 92 5/8 without specifying distance between countertop and upper cabinet.

I'd like to have 18" of space above the countertop. I can't decide whether the 18" should go to the bottom of the cabinets or the bottom of the light rail. I don't own any tall appliances. I just want whatever height will look best visually.

My calculation for top of upper cabinets:
36+18+39 1/8 = 93 1/8"

IKEA Home Planner software:
4 5/16 + 30 6/16 + 21 1/16 + 39 3/16 = 94 15/16"

IKEA official instructions: 92 5/8"

IKEA deco strip light rail: 2 1/4" - 2 3/8"

Any help would be greatly appreciated!