We find that some boxers, mostly men, get very competitive when being assessed. They want to beat their previous TUG or S2S or standing jump scores. The FaST assessment has 10 tests averaging 30 seconds each which is a net 5 minutes. Many of your boxers can be Superman for 30 seconds or even 5 minutes. However, they can’t keep it up all day, they would be exhausted.
The key for you is that they give you the same effort every assessment so the assessments are relevant to each other. But the assessments do not reflect what you see from them out on the floor. So, they might score a FaST score that seems to say they are Stage 1 or Stage 2 and you place them in Stage 3. The Superman Affect prevents us from numerically placing boxers in Stages. It is so tempting but it is unreliable.
You can't tell them not to do their best. You want them to realize that they can do more than their typical effort. And you want to know what their best effort is, so you know what to expect from them during workouts.
During the boxer's assessment consultation, you might tell them that you see the over-performance during assessments and that is good to see what they are capable of doing. Remind them that safety is important. And tell them you will be watching for more of their best during workouts.