I have tried to sort (Bars>Sort) my groups by "Group" and sub sort "Group" and "None" and the group order does not match Blizzard raid layout order. Most groups do, but some groups aren't in order. I've checked by even allowing duplicates in "Heal Groups" to make sure it wasn't main tank frames or pets.
Example is group 2. It is the only one that doesn't match the other sort order. (see attached)