When I load STL in parts into Slic3r v1.2.9 with "Load part...", how do I force it to think the bottom surface is completely solid? For example, add 1.stl to bed. Then use Load part to add 2.stl, which sits directly on top of 1.stl. How do I force Slic3r to think 2.stl is on solid surface no matter what 1.stl top layer is? Thanks, Danielby dlu3d - Slic3r