Have you tried DiskUsage? It's like SpaceMonger but for Android. In theory it should at least point you to the folder.
This app works very well, you just need access to a pc, with ADB tools installed to type in a simple ADB command. https://play.google.com/store/apps/details?id=com.rascarlo.granular.immersive.mode or, Tasker works well also. Either app needs the Write Secure Settings permission to do this. Tasker is useful for many other scenarios also.