ada-indent-handle-comment-special

ada-indent-handle-comment-special is a variable defined in `ada-mode.el'.
Its value is

nil

Documentation:
Non-nil if comment lines should be handled specially inside parenthesis.
By default, if the line that contains the open parenthesis has some
text following it, then the following lines will be indented in the
same column as this text. This will not be true if the first line is
a comment and `ada-indent-handle-comment-special' is t.

type A is
( Value_1, -- common behavior, when not a comment
Value_2);

type A is
( -- `ada-indent-handle-comment-special' is nil
Value_1,
Value_2);

type A is
( -- `ada-indent-handle-comment-special' is non-nil
Value_1,
Value_2);

You can customize this variable.