How to Change the Lumensity of the Ex Planet

The transit method has by far been the most productive. It works by leveraging the changing luminosity of the accretion disk orbiting and feeding the white dwarf. The theory here is that an x planet that is bound to a cataclysmic variable system oscillates the one legrange point between these three bodies, ok? Now this is the point, the grange points are were there's a gravitational equilibrium between various bodies. But why does it have to be a legrangian point? Wh can't it just be the orbital period of the planet itself? Because that somehow, that that legrange point is intimately related to this flow of gas, right?