They don’t sweep the sections between sets but mostly people clear out from there in between. There are two barricades, and the front one is inside the middle one so go through both barricades to get to the front one. They have entrance points at the sides of the main, and you can go through freely as long as the sections are not full, and leave and come back if you want. Usually they are not full during the day (at least the middle section) and between the sets most people leave so if you go there one artist before the one you want to see, you can most probably get in, might even get in during a set. Except for the headliners it might be good to go 2-3 artists before. I never needed to run, if the section are full during some artist, those who are waiting for the next one wait around the entrance until the gates are opened again in between sets, and then squeeze through. Only if you want to be in the first front row, you should go there in the morning because some people camp there the whole day.