delimit-columns-start is a variable defined in `delim-col.el'.
Its value is

Specify column number to start prettifying.

See also `delimit-columns-end' for documentation.

The following relation must hold:
0 <= delimit-columns-start <= delimit-columns-end

The column number start from 0 and it's relative to the beginning of selected
region. So if you selected a text region, the first column (column 0) is
located at beginning of line. If you selected a text rectangle, the first
column (column 0) is located at left corner.

You can customize this variable.