I believe if you first add a layer, then convert that layer for Smart filters, then apply the Lens Flare. You have some control over the flare now. Try inverting the mask and then click in the mask for the properties. Change the feathering and density until you get something you like. You can also paint in the mask to take away or add back You can also click on the little icon on the right to bring up the blending options for the filter. Hope I am understanding what your wanting to do. There is not a "flare filter" per se, there is Filter/Render/Lens Flare.