The term is named after the American policy analyst and former senior vice president at Mackinac Center for Public Policy, Joseph Overton, who proposed that the political viability of an idea depends mainly on whether it falls within an acceptability range, rather than on the individual preferences of politicians using the term or concept.[4][3] According to Overton, the window frames the range of policies that a politician may recommend without appearing too extreme, in order to gain or keep public office given the climate of public opinion at that particular time.[5] (wiki)
the problem is the Libs have got far right and stretched the frame beyond reasonable.
this is why the Labs have moved closer to the centre of the window. all the better to be seen due to the availability of the frame left by the Libs as they overreached and tried to pick up far right voters instead of focusing on regain the seats they lost.
the Libs would be "wise" to return to the window. let them look outside their own enclosed echo chamber and learn what people outside are thinking/saying. perhaps Ley will manage this.