The important thing to remember with all of Ganon's ledge tech is that the ECB (environmental collision box, what actually determines what you are "touching") is a
diamond shape. When Ganon double jumps, it
contracts a lot. When you airdodge, it instantly snaps to its
shape during the airdodge, which frequently causes it to collide with a platform below you, leading you to waveland. During a fp ledgedash, you are doublejumping until the bottom point of the ECB is above the stage and airdodging on that frame. Airdodging before then results in the point extending down beside the stage and you being pushed away, and waiting too long causes you to NIL onstage.
This is the mechanical reason why you can't airdodge sideways for a late waveland the way you can with diagonal airdodges; you are either above a platform and snap to it instantly, or you are next to one and your ECB collides with it (ledge) or the bottom point passes beneath it (platform).
For reference, here is the
dj ECB and the first frame airdodge ECB on top of each other. The distance between their bottom points is equal to the height above a platform you can be while airdodging, and that distance divided by Ganon's ff speed is the number of frames you have to press l/r for the perfect wl out of a ff dj. The same image for Ganon's
normal sh/fh and
backwards sh/fh demonstrate pretty well how much more difficult those are to perfect wl out of.
For reference, debug displays the current ECB as a yellow diamond, the previous frame ECB as orange. The white outline diamond is the "predicted" ECB, based on extrapolation from the previous frames, ignoring collision. I added the lines showing the past frame ECB behind the current ECB; the black line shows the distance between the lower points.
Also, I'm no Kadano; these are edited in MS Paint and could probably be a lot better/come with numbers instead of vague low res images.