I thought the overworld was capped at 30 million, not 32 million? That would make the Overworld 60 million across, and the Nether 15 million across.
Anywho, the width of the End has never been defined so as far as we know it's 1:1 to the Overworld. This might just be a case of "why bother?" given there was literally nowhere else to go in the dimension for like 85% of Minecraft's existence and even the gateway expansion hadn't bothered addressing this. It would be neat if it was defined as 8:1 (or at least some degree of expansion), though; that would make the Minecraft multiverse a series of concentric bubbles centered on the Nether, surrounded by the Overworld, which in turn was surrounded by The End (with the various modded dimensions being siblings to the Overworld and thus also surrounded by the End).
The Meaning of Life, the Universe, and Everything.
So I did it this is what happened. I built a portal at the nether border went through it and it spawned just barely inside the world border. I built another portal at the world border and went through it, it spawned really really far away from the nether border. I tried going through the first portal again brought me to the 3rd portal. I went through the 3rd portal again and ended up at the 4th portal. I went through the 4th portal again and it brought me to the 2nd portal. Short Version: If you build the nether portal first it will act like the nether is 1:1 to the overworld, if you build the overworld portal first it will act like 1:8 and teleport you far away from the nether border.
Fun Fact: The nether border is red instead of blue.
It followed standard portal creation algorithm. It took your nether coordinates, multiplied X and Z by 8. One or both of these were over acceptable limit so it adjusted them to be the limit. Then it looked for an active portal within 128 block radius of that spot, and finding none, created one there.