🚀 go-pugleaf

I am not certain I completely understand the problem.
Seriously - I am not being facetious.
When you say that you cannot clear the cache, this would be because the clear cache option is for removing unreferenced files. If the cache files are referenced in any saved project, then the Clear Cache item will not remove them. You would need to delete the cache to acheive this, and Encore would them simply rebuild it the very next time you launched that saved project and this would get very irritating whilst you wait for the cache to rebuild. It can be used in troubleshooting a project when a media file in the cache has somehow become corrupted, for example.
So - can you please explain exactly what the problem is? You should never see a completely deleted cache after closing Encore if there is any saved project. The biggest files here will be the conformed audio files, as Encore automatically conforms all audio files on import to 332-bit floating point. The rest are all quite small files in the main.

Might I suggest as another possible solution that you install a second HDD in your system, or a third one of you already have 2? Then you can place the cache files in a custom location, saving space on your C drive.