BuddyPress.org

CSS would work too if you want to override everything manually… but you might need to add !important to the declaration. I just did it in a function since my client will want to change the header image themselves from time to time and the custom header application would force them to crop anything they try to upload that is taller than 125.

So all I did was change the height definition (line 117 in bp-themes/bp-default/functions.php) by adding a functions.php file to my child with just one line:

define( 'HEADER_IMAGE_HEIGHT', 250 );

Seems to work.