Does Oracle's Block Change Tracking File Shrink?

4.4.4.4 Estimating Size of the Change Tracking File on Disk The size of the change tracking file is proportional to the size of the database and the number of enabled threads of redo. The size is not related to the frequency of updates to the database. Typically, the space required for block change tracking is approximately 1/30,000 the size of the data blocks to be tracked. Note, however, the following two factors that may cause the file to be larger than this estimate suggests:

• To avoid overhead of allocating space as your database grows, the change tracking file size starts at 10MB, and new space is allocated in 10MB incremenents [sic]. Thus, for any database up to approximately 300GB the file size is no smaller than 10MB, for up to approximately 600GB the file size is no smaller than 20MB, and so on.
• For each datafile, a minimum of 320K of space is allocated in the change tracking file, regardless of the size of the file. Thus, if you have a large number of relatively small datafiles, the change tracking file is larger than for databases with a smaller number of larger datafiles containing the same data.