I am no designer, but I love studying design. I would say make the bottom edge of the fixture level with the bottom of the top half circle window or centered on top window. (It must be at least a foot higher than any person that may walk underneath) - not sure your ceiling height.
I have a similar entry. my chandelier is centered on the upper half circle window. But my ceiling height is two story at the entry.

I would keep the bottom of the fixture about 7' off the floor.

centered in upper transom