Note about Lylat's tilting stage:
Some moves will follow the contours of the stage while others will always act as if Link is standing on a flat surface. When you're facing down-hill for example, F-tilt won't hit as low at full reach because it will continue to act the same as it would on a flat surface, but of course if you're facing up-hill, it will hit much lower below stage than usual. D-smash on the other hand will adjust where it hits in relation to the surface it is used on (except on extreme slopes; it has a limit to how far it will adjust), so on Lylat it will always hit at the same distance from the ground regardless of the slope.
Because characters hanging on ledges behave as if they were hanging on a ledge attached to a flat surface, D-smash will actually hit 'lower' in relation to them, even though it is hitting at the same distance away from the line of the stage.
Because the outer edges of Lylat are at an angle, the tilting of the stage will never actually fully compensate for it and so you'll never actually be able to take advantage of F-tilt hitting lower than usual. At best the outer edges of the stage will always have the slightest slant downwards, even when the stage is fully tilted the other way.
With that said, when trying to hit people who are recovering or hanging on the ledge or in that general area by the ledge, you'll probably want to favour either the first or second hit of D-smash except when the stage is tilted all the way up; only then will F-tilt hit lower than D-smash as usual.