Help w/Elliptical Marquee Tool

My goal is to simulate light shining on the side of a building by using an elliptical marquee and a curves adjustment layer. However, when I draw out the ellipse and try to adjust its position using the Free Transform, it seems I get an overlap of the new position with the original position. It seems what I have to do is to apply the original ellipse to the curves adjustment layer and then do a Free Transform on that mask layer. Is this the only way or is there a better and different way? Thank you.