The design of tactile graphics for blind and visually impaired students generally adheres to standard design guidelines written before modern technologies, when producing "volumetric" (with variable heights) tactile diagrams was difficult. Thus, the perceptual-cognitive dynamics of volumetric tactile elements are not thoroughly understood. This work explores the use of volumetric elements for creating effective tactile graphics through several experiments conducted with individuals with blindness. The results indicate that variable heights can effectively and intuitively convey several kinds of information, particularly in quantitative diagrams, charts and maps with discrete, clearly contoured sections representing different numerical or spatial values.