I have some other information about the snapshot capacity. During an Acronis image backup from my laptop to an external disk this afternoon I did some windows updates selecting the updates in 4 or 5 runs. Each run created a restore point. In the vssadmin shots I attached you can see the increase of the shadowspace. I noticed that even when no restore point was taken the shadowspace grew, probably due to the image backup running. Suddenly after a while, the backup was already finished at that time, the last restore point forced a delete with a volsnap event id 25 in the system eventlog. See attachments of the System and Application eventlogs. Now I know the boundaries of the used and allocated shadow spaces.
Used space : 350.22MB, Allocated space : roughly between 729MB and 800MB. Beyound that both used and allocated space is flushed and deleted. How is that possible with so many room available!!! The Max shadow copy storage was set to "Unbounded" during this test. There was 11Gb free space on the disk. See attachments.