Any hints I missed? *spoilers*

[Clord]

looking up, the most underestimated puzzle mechanic ever made, you'd be amazed at how easily people are stumped when something is above them, so i have a plan, whenever i get stuck on something, i take a good long look at the ceiling.

One of the Portal's Commentary Nodes mentions how they dumped down at least one of the puzzles because at least some of the beta testers didn't realize to look up.

This bring me to another point about how nicely detailed those high ceiling rooms are and almost nobody pays much attention to those ceilings.