The normal operation is to maintain the case of the Author (or Title) field, when calculating the Sort. (the box will turn Green in the MDE)
In the MDE, you can: Right click: change case: <select>
Note: the box will turn Red (does not match the parent).

You can also perform this change (change case of the author_sort) via Manage Authors. Righ-click in the
Authors section of the
Tag Browser:
Manage Authors
AFAIK nothing prevents the sort value from being 'repaired' when adding additional books by that Author or future MDE actions