Just found a bug in Stablebit Clouddrive (1.1.0.1038 RC):
When you create a new drive (I'm using Google Drive), you can set the cache size to 1TB, 2TB, whatever, as long as theres enough space on the selected cache drive.
But if you de-attach the drive, and re-attach it - the cache size cannot be larger than 500GB even if your cache drive is larger than 500GB.