You have to understand what this ellipsoid actually means. It's an approximation of the object itself, that it more are less accurate, depending on the object. 20,20,20 makes no sense in your case, because while the bed might be 20 wide and deep, it's for sure not 20 high. And if you start with an ellipsoid that's already in a collision, because it overlaps with the rest of the geometry in some way...well, that's not a good idea, because ellipsoid collision detection is a collision AVOIDANCE algorithm. It's not very good in resolving collisions that are already present when you start.
So: Find an ellipsoid size that matches your mesh and doesn't intersect with the rest of the world right from the start. If it helps: There's a createEllipsoid()-method in the ExtendedPrimitives class. Create one with the same size as the one that you are using for your collision, add it to the world and as a child to you collider, so that you can actually see, how your choosen dimensions look in action.