The "$22 of ikea parts" approach looks like a torture device to me.
The tiniest tweak to standing desk height can make a big difference in resulting posture and comfort. (My exact height preference even changes from day to day, perhaps due to varying shoes or recent levels of other activity.)
It's not strictly modal, "when doing X use height Y" – I just find my posture preference changing slightly over time.
I suppose long writing/coding is a bit more active/upright (higher), while long reading/browsing tends to involve a forward or alternating side-lean (lower). Shoes, time of day, and other recent exertion seem to be factors as well. And I alternate to seated, for hours or sometimes days at a time, for variety.
I suspect I'm more likely to start a new project or do many small independent tasks while standing, and more likely to work-through a lengthier, involved task while seated... but I haven't kept careful notes.
The tiniest tweak to standing desk height can make a big difference in resulting posture and comfort. (My exact height preference even changes from day to day, perhaps due to varying shoes or recent levels of other activity.)