show-paren-style

show-paren-style is a variable defined in `paren.el'.
Its value is

parenthesis

Documentation:
Style used when showing a matching paren.
Valid styles are `parenthesis' (meaning show the matching paren),
`expression' (meaning show the entire expression enclosed by the paren) and
`mixed' (meaning show the matching paren if it is visible, and the expression
otherwise).

You can customize this variable.