How can I change the default subscript position and size for Impress?

I would like to be able to change the position of subscript text in Impress, since the default position and size cause the text to be too low, resulting in lines of text being unevenly spaced. In Impress, there is no way to control this with Styles. One must simply set the value every time.

Can someone tell me where the default size of 58% and position of 33% are defined? Is it in in the XML of the current document, in a system-wide configuration file, or hard-wired into the source code? Even if it’s in the source code, it’s OK! I will submit a bug request and try to get it changed. But I can’t even find where that default value comes from at the moment.

I am using LibreOffice on Ubuntu 18.04.

Ping, does anyone have any answer to this question?