>My understanding is the correct, ergonomic distance your eyes should be from a monitor is about 1.5x the monitor's diagonal measurement. With 22" or 23" monitors, that's too far away for me to reach the screen at all, let alone work comfortably with one using touch.
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>For comfortable manual use, you really don't want a touchscreen to be any further away than your keyboard or mouse. That implies the maximum useful or ergonomic size for touchscreen monitors is actually pretty small.

I'd hazard a guess that the 1,5 norm was devised under different circumstances, namely that you should see the whole desktop at once and easily switch your eyes from menu to status bar and back. Now with larger monitors (like the one 20" and one 21" that I have, the larger one being vertical on the right), I never even try to see even one whole at once, even though I keep them within hand's reach (roughly 25"). They're like a desk. Imagine you're doing something with your hands, standing next to a table, and your material and tools are spread across that table. Doesn't feel unnatural in any way (except you need to bend or walk around the table at times) and you don't even try to see the whole table at once. If you lose a bit, you may criscross the table with your eyes, so what.

Having your tools spread over a surface larger than this 33-degree angle that follows from the 1/1.5 ratio of width/distance is not uncommon at all. It's only the area that you can see at once, but is that really a requirement?