Spatial Contact Force is causing my model to fly into space

The spatial contact connected to several spherical solids (circled) is connected by the geometry port to an infinite plane, which is the dotted line. Because of where Matlab puts the initial spacial conditions, the model always jumps from the -Z side of the plane and flies off to the +Z side of the plane, never falling back to the ground.

How do I tether the model to the ground, or at least, make the model start in a more stable initial condition?

Thanks