Well, use the edit menu and the move functions and keep moving it back until it's actually behind the terrain. You'll have to keep resizing it, but that's no biggie. A lot of placement in Bryce is hard to do because you can't move the overhead shot to show objects that are out of the camera view from abve. But if you have shadows turned on, and use the moce function, and do partial renders now and then, you can get things about where you want them. Mainly it takes practice in reading the wire frames and learning how to use the move arrows in the edit menu. Collision detect helps for placing objects on the ground or on other objects, but objects in Z axis are hard to place until you get comfortable with the move functions.

Talent is God's gift to you. Using it is your gift to God.