I watched a video with someone loading a radial extractor and saw 3 different styles of side bars on the frames.
pause the video then skip to 1:31 to see the frames I am talking about
https://www.youtube.com/watch?v=ZRA808I62W4
You will see a dark frame with straight sides, next to that will be 3 with a long taper then 1 with a short taper then more dark frames with straight sides. What difference does the geometry of the sides make? Maybe some are easier to uncap with automatic machines or remove less wax? Allow the bees to walk around the frames more easily?