Peramlinks prefixed with ‘/blog’

After a fresh installation (2.9.2) I wanted to change the custom structure in the Peramlink Settings. However, the custom structure text field (also same for category base and tag base) is prefixed with an uneditable ‘/blog’.

This prefix does not appear (nor mentioned) when reading the codex or watching video tutorials.

Is it possible to edit or remove this prefix? Changing the ‘permalink_structure’ option_value in the _options table did not produce the desired result.