I had come up with this theory earlier, but confirmed it while talking to a SP trooper today.
This only relates to multi officer speedtraps. The trypical scenario being one shooting LIDAR, the other(s) writing tickets. Say for this example it is a 55 zone. When they first setup they will start by tagging cars at 75, however as the line starts to build up (they can only write tickets so fast) the shooter will raise the window. So after they get two or three cars parked and the other trooper writing citations, the shooter will up the window to say 80+, then if they get a few more cars he will only tag for very high speeds like 85+, until they finish with the other cars.
Another interesting thing is on some of the smaller traps with just a shooter, and ticket writer, they won't pull over cars in the right lane (unless the speed is absurd) on 3+ lane roads. Assuming they don't have a chase car. This is because the shooter (in the median) can't point the car in the left lane over without causing a huge traffic problem, and typically the other officer is busy writing citations, so they won't bother.
Just figured I share the info. Lessons, stay in the right lane as much as possible if they set up speedtraps in the median in your area. Also don't be the first one into a speedtrap .