S2 missing cloudy pixels in mask

I have downloaded SNAP and sen2cor to my fedora distribution and followed the installation guide but i feel i’m missing something as when i try to mask an image with either cirrus or cloud cover it doesn’t capture all or even most of the cloud. For example this is my image and in red is what has been detected as cloud cover even through there is clearly more. I’m very new to SNAP and sen2cor so i’m not sure where i went wrong. I’m using S2A LC1 images.