[xmonad] Behaviour of window stack when closing a window

Hi! When closing a window, the focus goes to the next window in the stack, if it exists (e.g. "head $ down currentStack"). What is the best way to change that behaviour to let the focus go to the previous window in the window stack (e.g. "head $ up currentStack")? (btw: This is my first post to a list using a newsreader client, so: Am I doing this right?) Thanks, Sönke