Calculating ratio for very strick tracker

In order to prevent cheating peer in closed tracker, there is a very easy solution to solve this problem. However, it might be too strick. Problem: Some clients do not even try to contact tracker but they are still able to leech using historical peers information. Solution: Count amount of download by size of the torrent immediately when download its metadata Advantage: Disable cheating of unreporting clients Disadvantage: Downloading only some files may not fair