I’m using 36” fixtures on my 80g & 60g tanks, both tanks have a 2’ x 4’ footprint and both are AIO’s. Because the are AIO’s the display is only about 42” but like Justin stayed the far sides will be great for lower light corals.
Feel free to come by and see how the light spread works from a 36” fixture, how I have mine set up may give you some ideas.