Since moving an old file into a directory modifies the directory, it "w" timestamp is changed. 99.9% of my accesses do not care what the directory dates are, only files. The complimentary issue is even worse - let directory A and its subdirectory B be older than the date range of interest, but let B's subdirectory C contain a file in the selected range. It will not be reported!
Since the issue is raised relating to @FILESIZE, not @DIRECTORYSIZE, I would like to see the DESIGN changed - when a request is made for members of a directory hierarchy within a specific date range, ALL matching members should be included, even if there is a directory level in the path to the matching member which does not match. I would compare this to trying to locate all 25-year old soldiers in a batallion, and the report ignoring the 25-year olds in units whose commander is older or younger.