In this experiment, falling particle trajectories within and without a glass box placed on the lower electrode in a Gaseous Electronics Conference reference cell are recorded and analyzed, and the electrostatic forces exerted on the dust particles are measured and compared. Experimental results show that, for particles falling in a complex plasma with no glass box, only a single force balance point (i.e., the position where the gravitational force is balanced by the electrostatic force) exists in the vertical direction while, for particles falling inside a glass box, this force balance spans an extended vertical range.