? I think you misunderstood what I was saying.
What I meant was that Ganon is most likely just always very slightly lower than the opponent when going down (the amount varying slightly from character to character).
If the distance they both move downward per frame is greater than the distance that separates them, it allows for sometimes having them both cross the blastline on the same frame, while other times Ganon crosses it 1st while the other is still very slightly above it and would have died on the following frame.
The closer they are together vertically when that char is held the more frequent SD occurs, and being further apart will result in Ganon dying 1st more often against that char up until the point where a char is held further apart than the distance they both travel per frame which would always result in Ganon dying 1st against that character (if there are any like that).
In the case of them both crossing it on the same frame in sudden death mode, then it would indeed go by controller port priority. Otherwise normally, it would result in a loss for Ganon if they both don't cross it on the same frame, and sudden death if they both do cross it on the same frame.
Basically, if able to get either SD or a loss for Ganon against a char on last stock, which one you get in a normal match would be dependant on where in the air it connects vertically with respect to the blastline. Since a few pixels could make the difference between crossing simultaneously or dying first by the time you reach the bottom, it wouldn't be something you have realistic control over in general. However, depending on the character you may have certain percent chances on average to SD or lose against them.
For example, say against Char A who is held closer to Ganon, you get about a 70% chance to go into SD and 30% chance to die first. While against Char B who is held a tiny bit higher than Char A you may have about a 40% chance on average to go into SD and 60% chance to die first.
You may also be able to get more controlled outcomes if able to ensure you connect it at a specific height of the stage, such as ledge hopping and performing it at an exact height. This would depend on the stage and character. If this is indeed how it works and there are no other small factors playing into it, then it may be possible to guarantee a result this way in some situations. Like say if you ledgehop perfectly on (Smashville) and connect a F-B from exactly at the peak of your jump against (Wario) you'll be positioned vertically so that you'll both cross the blastline at the same time or something.