Spotlight light function question

Suppose I have a spotlight shooting to a plane with some circle as light function. In the center of the plane, I should see the circle as circle at the border of the plane, I expect to see elliptical rather than circle but I found it is still circle. Where should I change?

can u upload render or snapshot.

This is the light function projected from Spotlight to a plane. I expect elliptical at the border but it is almost the same as the light function, still circle everywhere.

may i know what is purpose and what result you r looking for. bcoz light function used to projection.

I draw this light pattern to test if the circle deforms as what I expected. I use different size of circles to test if it is size dependent( e.g., insufficient resolution may cause some misleading results). I assume the light function is something like shooting the plane with flash light as shown in the attached image, d1 > d0 that cause circle becomes elliptical when shoot at angle.

hmmm. i think u should google on this. u can see i used ligh function for water caustic.