Pop quiz: Transform in the inspector window

If I have a 1920x1080 composition and I want to put something at the top right corner, I set the position to 960, 540, which is 1920 / 2, 1080 / 2. So far, so good. Well if you're so smart, how abaout if I have a 512x512 composition, what should I use as the coordinates for the top right?

• 256, 256, of course.
• ahh, 960, 540 maybe?
• 256, 455.111
• Agh I give up, just do it by eye?

So who guessed 256, 455.111? I mean it's obvious right? Seems like you have to multiply the coordinates for the y position by the aspect ratio of a 1920x1080 frame. 256 * 1920 / 1080 = 455.11111. Why? What exactly is going on in the head of whoever came up with this cursed nonsense?
I mean I can get behind Fusion using normalised dimensions, where the top right is [0.5, 0.5], and I can get behind absolute pixel values, where the top right in a 512 square frame is [256, 256], but this is just garbage.
No wonder Resolve has such a bad rep for motion graphics.
Now your homework is: tell me where I should put a piece of footage if I want it to fill the left-hand third of a 10800x1200 frame, and what the scale should be.

Well that's me stumped. I did it by eye, first by finding out what the left and right side of the comp was, which turned out to be 27337.5 and multiplying it by 2/3 to get 18225. How that relates to the size of the comp, the size of the footage, a standard HD frame, the aspect ratio, or the number you first thought of completely eludes me thus far.