Wrong column reported for errors in function sig type comments

For the following code

def extract_commit_hash(line):  # type: (str) -> Optional[str]
    ...

def extract_commit_hash2(line):  # type: (str) -> Optional(str)
    ...

mypy reports wrong columns:

mypy output:

> mypy --pretty --follow-imports skip --show-column-numbers --show-error-codes wrong-col.py
wrong-col.py:3:10: error: Name 'Optional' is not defined  [name-defined]
    def extract_commit_hash(line):  # type: (str) -> Optional[str]
             ^
wrong-col.py:3:10: note: Did you forget to import it from "typing"? (Suggestion: "from typing import Optional")
wrong-col.py:6:10: error: Invalid type comment or annotation  [valid-type]
    def extract_commit_hash2(line):  # type: (str) -> Optional(str)
             ^
wrong-col.py:6:10: note: Suggestion: use Optional[...] instead of Optional(...)
Found 2 errors in 1 file (checked 1 source file)

From what I found the reported column is always 10 even if the code is more indented.

Reproduce the report with the shown wrong-col.py example and the mypy command using --show-column-numbers. Trace how diagnostics for function signature type comments calculate their column, then verify that errors in differently indented functions point to the relevant source location rather than a fixed column.