I was involved in Farnborough sleep deprivation tests over 2 days about 25 years ago. The results were startling. Performance improved greatly in a fatigued situation- I assume because you are tired, you give full attention to the test or task without distraction. However the moment the task became boring or repetive, you rapidly lost it, and even conked out unconscious. But the actual simulator tasks (bombing a target on a bearing and distance from a point at a particular time) was enormously improved after sleep deprivation.
I don't believe silly little tests will tell you how tired you are. When enormously fatigued, you have 100% efficient modes interspersed with periods of enormous tiredness and lack of concentration.
I don't know why we bother with the EU. Quite simply the politicians have been dictated to be the big airlines, and what is good for the pilots (and passengers) has not really been considered.