I cannot find a method to change the predefined values for sub- and superscript.
There are many resources that
1. complain about the unfeasible default values
2. suggest to modify the underlying format
The latter doesn't work here, since
1. there is no more text style, only paragraph style, and
2. the 'style' editing widget does not have a tab for 'position', contrary to the Format->Character. Without that, there is no way to modify the position, at least as far as I can make out.
The only 'workaround' is to manually format all occurrences (in my case hundreds).
Please see my comment 5 in bug 89849 for a workaround using find & replace.
*** This bug has been marked as a duplicate of bug 89849 ***
Yep, I misread my own comment as the workaround was only for writer.
So let's set this as a dupe for another report.
*** This bug has been marked as a duplicate of bug 40871 ***