A reach truck is more stable when the forks are retracted as the load center at this point is usually situated within the reach truck's wheel base. As the forks are extended, a counterbalance situation starts to develop. On most reach trucks, when the forks are fully extended it becomes a counterbalance type truck without the benefit of any additional counterweight. The weight of the truck is usually the sole counterweight.

Pick up a 40 pound sack of cement and standing upright hold it close to your chest. You are fairly stable in this position as the weight is within your body's stability base. Standing upright, hold the sack of cement in your hands and slowly extend them. The further the sack extends from your body the less stable you become. The weight of your body is your sole counterweight

An empty reach truck with the forks retracted is less stable as the truck's center of gravity shifts toward the narrow portion of the imaginary stability triangle. Less dynamic force from braking, turning, shifting loads, etc. is required to shift the reach truck's center of gravity beyond the imaginary stability triangle.

Lifting personnel in a work basket with the reach truck forks extended is definitely an unsafe act and an accident waiting to happen.