org-edit-src-content-indentation is a variable defined in ‘org-src.el’.
Its value is 2
Indentation for the content of a source code block.
This should be the number of spaces added to the indentation of the #+begin
line in order to compute the indentation of the block content after
editing it with ‘M-x org-edit-src-code’.
It has no effect if ‘org-src-preserve-indentation’ is non-nil.