12.5 % of contiguous space on a volume is reserved for the MFT.
   This protects against fragmentation of MFT 

   Smaller files stored in MFT.

   If MFT fills, 
     another large contiguous block will be allocated and converted to MFT.

   If MFT entries are freed, 
     they will be marked but storage is not returned to general use.

   However, this may cause slower disk access. 

   Its possible to change the default size of the MFT when formatting volume.
   4 setting possible with various initial MFT sizes. (1 is 12.5%)
     Use "fsutil behavior query mftzone" to find current setting.
       if blank, then 1

     1 = 12.5% (8K files)  2 = 25%  3 = 37.5%   4 = 50%
     It should be increased of a large # of small files to be stored.

     This can be adjusted after a volume is formatted with limited results.
       MFT cannot be made smaller the default calcualated by OS.

       Reducing size will free unused MFT space but not used space.

       Additional requested MFT space will not be contiguous with original.

 If extended attributes stored in general storage or user data use up available
 space, 
   OS will reclaim some of the MFT reserved space.