compare-windows-recenter is a variable defined in `compare-w.el'.
Its value is

List of two values, each of which is used as argument of
function `recenter' called in each of two windows to place
matching points side-by-side.

The value `(-1 0)' is useful if windows are split vertically,
and the value `((4) (4))' for horizontally split windows.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.