small files are same but not affected because it's rare to stop defragment in the middle of small files
for a big file, each time you stop (not pause) and and defrag again on the specified big file, you start from 0%
this is not a display issue, say it already done 50% but when it re-do the remaining 50% it show 0%. it simply start over. i'm sure about it because i can see the drive map seeing that previous moved to, is still being read from
this is not only a stop/resume feature request which you may claim not supported, it's defrag poor speed which mean the whole file need to be moved to a whole new place even if there's enough space after the fragment
let's say, number=space, letter=data
fragment a=1 | b=_ | c=2 | d=3 | e=_ | f=_ | g=_ | h=other
i think is can and should only move 2 to b, 3 to c