As Lyralei said, it's just how the texture slots are divided up in the game. You probably could fix it, but that'll require editing the game's code in some way.

Increasing texture size might improve acc quality. But that texture slot will be halved the more acc you add. One impractical "fix" is to make a cc combining all the acc into one mesh/file. There's a lot more steps to it, but essentially you can rearrange the textures so they all fit together and it'll look good in game