csmertx: my tent preference is to rotate about 40–50° up from horizontal. But really, anything above 10° should make a big improvement compared to flat.
The reason to tent a keyboard is to reduce the amount of wrist pronation required while typing. The wrists’ relatively neutral/relaxed range is probably something like 30–90° [caveat: I’m not a doctor or physical therapist; look up a textbook for some more precise biometric measurements]. When you pronate your wrist, it puts quite a bit of static load on several tendons/muscles, and also stretches out some tendons which you need for finger movements, giving them less strength and flexibility. Similar story (though probably even worse) for flexing or extending your wrist. The discomfort which results encourages typists to stick their elbows out to the side to flatten out their forearms as a way to reduce the amount of pronation, but this in turn puts a lot of additional stress on the upper arms and shoulders which have to hold up the weight of the arm. Instead of having their arms free-floating, typists then rest their elbows, forearms, or palms on an armrest, palmrest, or the table, which limits the ability of the big muscles in the upper arm to contribute strength or absorb shock.
If you tent the keyboard even a little bit, it makes a big improvement to basically every other aspect of your arm position and posture. Even if you don’t get the wrist to be completely neutral, you’ll still be dramatically reducing the static strain from typing.
But as TP says, a very aggressive tent will get you closer to a completely relaxed posture.
