And #6 mentions "the power that you can routinely generate during long intervals done in training." A 20 minute interval counts as a "long interval." If after your test, you end up with a number you can't routinely do in training, then modify it accordingly.

Note that, as per the test in _Training and Racing ..._, it's a good idea to do a 5 minute all-out effort, then a 5 minute rest, then the 20 minute test. This minimizes the affect of your AWC on the 20 minute test.