Exactly. I let it pool at the edge where the lip is. I also let it fill deeper than I'd ever want a wedge thick, then shape and thin with the belt sander... Which is its own bit of work! I drill a hole through the piece of material, put a pin into a small bar of aluminum, stick double-sided tape over the pin, then affix the wedge material to the tape so the pin goes through the hole. Without the pin the heat can loosen the tape enough to pull the work piece off, but it keeps enough hold to prevent it from rotating around the pin. Without the tape, the pin can't keep it from rotating when you change the angle of grinding, so you need both tape and pin.

As for best guess... It doesn't need much. On a standard baking sheet, raising one end up about an inch should do the trick. I used a bigger angle, so I have to change it with the belt sander on every piece I make. :P