The "Extended" ADF file format is used for games you may download at the Factor 5 homepage. These files contain some tracks which are specially encoded. This includes Turrican 1, 2, 3 and B.C. Kid.
These adf files aren't ripped from a real disk, so don't bother discussing the different sizes.
The fact is that these adf files can't be written back to a real Amiga disk.