didr on "How to override args of 2013 for custom-header from child theme"

I put in the functions.php of a child theme of 2013 the code

function twentythirteenchild_custom_header_setup() {
	$header_args = array( 'height' => 182,
						  'width' => 940);
	add_theme_support( 'custom-header', $header_args );
};
add_action( 'after_setup_theme', 'twentythirteenchild_custom_header_setup' );

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for changing the width and height of the header but it didn't work. What is wrong?