The thicker a plate is, the greater the circumference of its outside surface in relation to the inside surface when it is mounted on the cylinder, which in turn causes plate distortion to increase. Because flexo plates are relatively thick, ranging from 0.030" (0.75 mm) to 0.275" (7 mm), the magnitude of this distortion can be substantial, making compensation for it critical to the production of quality presswork.
Flexo printers normally have existing lookup tables that indicate the amount of distortion to apply for each media. These lookup tables include distortion compensation amounts for every different press cylinder diameter, or repeat, that a given flexo printer uses. All you need to know is the repeat length, or number of gear teeth in the cylinder, and you can look up the distortion factor to use.
For details about how distortion factors are determined, see How is distortion compensation calculated?.