Perch have a finite life span. So key variable is food. Every perch will grow huge with unlimited food. When food is limited they stunt or in other words stop growing at about 6 inches to allow for more individual per square cube of water.
What limits stunting can be winter or summer kill or predation.
Walleye and pike and other perch eat perch naturally. Grebes, mergansers and lions eat perch.
People catch perch.
In my little experiment we had tons of perch within casting distance...all stunted. We fished them hard removing thousands upon thousands. Just in an area about 100 feet X 100 feet. Now we catch 9 and even 10 inchers. Not a ton but we have seen a size increase for sure.
It is true they have bigger fish further south and because of the mix of predation and growing season.
Good predator / prey balance allows for normal year class development.