Trick feels a bit different depending on the obstacle, on a rail will feel more like a balancing act whereas on a ledge there is resistance and friction around your back wheels, normally slowing you down but that's also space to distribute more of your weight over that you normally don't have (pushing down on the back leg on a rail lipslide, you'd just tip over to the other side, whereas here you can use the assist). Even if your ledge is waxed, you'll need or at least want speed. Maybe don't try to pretend you're doing the same thing you'd normally do on a rail and instead approach the trick more like a frontside disaster on transition if that makes sense, you kind of bash into it then endure.