Reflexes are associated with brain activity. Faster tempi increase brain activity due to the higher frequency of the beat change, this requiring system 2 thinking enabled more actively. When used as a background for any other action, this affects the overall brain performance in the background, leading to inconsistency of performance between the start and the end of any action.
This piece is more appropriate for this kind of situation, as it's not too repetitive to bore the brain out, nor too complex to tire it. As a result, the brain is being affected in the background from a noticeable adjustment that doesn't require too many resources for processing. And that concludes us to the variance in reflex performance.
Also, nice track. Glad to see you alive, hope your research goes well.