To access the global brush dimensions, double click on tool, on warp tool for instance. From there, change the sizes of width, height, angle etc. Another way to change the mass distortion tool without to open this settings box, is to use two keyboards: SHIFT and ALT. Press the SHIFT+ALT key and move the mouse to change the size of brush. In case you need to change and the angle of brush, then press just the ALT key and move the mouse along x and y axis to achieve the wanted angle.