First thing the middle of the volume/partition is not the middle of the disk in any multi-partitioned disk, then NTFS $MFT is not (and never has been) in the middle of the partition, its location varies depending on the size of the volume/partiton but above a certain size, around 5/6 GB it is at a fixed offset, usually on LCN #786432 which - on a normal 8 KB/cluster NTFS volume - amounts to offset 6,291,456 sectors or 6,442,450,944 bytes, rarely the middle of the volume, unless its size is around 13 GB.
Seems to me the MFT was in the middle of volumes commonly in older versions, and lately much closer to the beginning of the volume.
Could have something to do with the feature of shrinking a volume which became more common, and you can now more often shrink an NTFS volume by more than half, which was often impossible in earlier years.
If you "think in hex" the address is in the PBR expressed in clusters (VCN) as "0xC0000" (at offset 0x30 or 48 dec you should find "00000C000000000"), which is a nice, round number.
Maybe you remember the "old" NTFS format (NT 3/4) where the mirror of the bootsector (aka $BootMirr, not the $MFT)was exactly in the middle of the volume, but since Windows 2000 this copy of the first sector of the PBR was moved in the "gray zone" at the end (inside the partition but outside the volume[1]).
As a side note (and JFYI) thanks to (from 7 onwards) NTFS resizing capabilities it is possible to "force" the $MFT to very early sectors, see this only seemingly unrelated thread here:
http://reboot.pro/index.php?showtopic=18022
[1] some info on the matter in this other, as well seemingly unrelated, thread:
This now makes me wonder whether the middle disk block (numerically) is equal "seek times" away from disk edges.