Your categories separate items by type but not by similar stack sizes. So the ore/plate/item stack size modifier sets all ores, plates, barrels, circuits, etc. to the same value, even though the default value for ores is 50, plates is 100, barrels is 10, and green circuits or copper cables is 200.

I think it would make more sense to separate by similar stack size categories, or at least to make a larger total number of categories.

I made an unofficial update: https://www.dropbox.com/s/cmdiig4t27v0jxb/Custom-stack-sizes_0.2.0.zip?dl=0

You can have it if you want it, or you may freely copy code from it into your official mod. I've barely tested it but it runs and seems to work at a glance. I also added motor to the list for the motors in Earendel's mod AAI Industries.

This was intentional for making them all the same. I do want to add more categories but it is difficult to define hard categories unless I go off of the vanilla stack size. I've been working on trying to separate them more without adding too many extras. I know instead of using flat values I could use multiplier values for their stack sizes but I still wanted to be able to allow people to change the flat stack size of all and I've been working on a solution to implement both.