Hide admin sidebar by default

[bear]

Just moved to the latest WHMCS, and a lot of my older hooks no longer work correctly. A basic one would be to hide the admin sidebar until I click to expand. 
The code below was working (courtesy Brian!). Now it hides the content, but the sidebar still takes up the space it would occupy (blend template in admin).

function hook_admin_minimise_sidebar($vars) 
{
    return array("minsidebar" => true);
}
add_hook("AdminAreaPage", 1, "hook_admin_minimise_sidebar");

Have I missed something? Hs this hook point been changed? Docs don't specifically mention this, but the hooks don't seem to have significantly changed between versions.
I have several other useful hooks, and all seem to be non functional.