Finding the optimal pace in any competition is no easy task. It is not the Holy Grail either, but we must recognize the enormous difficulty of knowing if we could have done better (except in those circumstances in which it is flagrantly yes).
For this reason, finding that exact point of suffering is certainly complicated and more so the more variable and the longer the competition. It is also not the same to manage a race for a leading competitor, than one who is going to look for his best time or one who is going to simply finish.
In order to be able to manage competitions correctly, we simply need to have a correct reference in terms of the functional pace/power threshold. From that point, we must modulate our effort according to the length of the race. In this way, we ensure that we can sustain the intensity from start to finish without melting down beforehand and arriving on foot or crossing the finish line without giving away performance.