A window covering assembly for an architectural opening such as a window, said window covering assembly comprising - a first or top movable rail having left and right longitudinal ends (103A, 103B), - a second or lower movable rail having left and right longitudinal ends (105A, 105B), - blind material connected to the two rails (103, 105) and extendible and retractable between the two rails (103, 105) by moving one or both rails (103, 105) away from or toward each other, and - a pair of first and second main tension cords (109, 111) routed in mirror image one to another from the top movable rail to the bottom movable rail, through and along the top movable rail, the blind material and the bottom movable rail; wherein: the first cord of the pair of the first and second main tension cords (109, 111) is routed to enter the top of the top movable rail at a first entrance point which is adjacent one of the left and right longitudinal ends (103A, 103B) of the top movable rail and spaced a first length measured from said one end; the first cord is then routed through or along the top movable rail to exit the bottom of the top movable rail at a first exit point which is spaced at a second length measured from said one end, the first length exceeding the second length; and the first cord is routed to enter the bottom movable rail at a bottom rail entry point directly opposite to the first exit point of the top movable rail, is routed through or along the bottom movable rail and exits the bottom movable rail at a bottom exit point at or adjacent the other end of the left and right longitudinal ends (105A, 105B) of the bottom movable rail. - a first or top movable rail having left and right longitudinal ends (103A, 103B), - a second or lower movable rail having left and right longitudinal ends (105A, 105B), - blind material connected to the two rails (103, 105) and extendible and retractable between the two rails (103, 105) by moving one or both rails (103, 105) away from or toward each other, and - a pair of first and second main tension cords (109, 111) routed in mirror image one to another from the top movable rail to the bottom movable rail, through and along the top movable rail, the blind material and the bottom movable rail; wherein: the first cord of the pair of the first and second main tension cords (109, 111) is routed to enter the top of the top movable rail at a first entrance point which is adjacent one of the left and right longitudinal ends (103A, 103B) of the top movable rail and spaced a first length measured from said one end; the first cord is then routed through or along the top movable rail to exit the bottom of the top movable rail at a first exit point which is spaced at a second length measured from said one end, the first length exceeding the second length; and the first cord is routed to enter the bottom movable rail at a bottom rail entry point directly opposite to the first exit point of the top movable rail, is routed through or along the bottom movable rail and exits the bottom movable rail at a bottom exit point at or adjacent the other end of the left and right longitudinal ends (105A, 105B) of the bottom movable rail. the first cord of the pair of the first and second main tension cords (109, 111) is routed to enter the top of the top movable rail at a first entrance point which is adjacent one of the left and right longitudinal ends (103A, 103B) of the top movable rail and spaced a first length measured from said one end; the first cord is then routed through or along the top movable rail to exit the bottom of the top movable rail at a first exit point which is spaced at a second length measured from said one end, the first length exceeding the second length; and the first cord is routed to enter the bottom movable rail at a bottom rail entry point directly opposite to the first exit point of the top movable rail, is routed through or along the bottom movable rail and exits the bottom movable rail at a bottom exit point at or adjacent the other end of the left and right longitudinal ends (105A, 105B) of the bottom movable rail.