For some time now I have been unable to determine why my brush or eraser tools do not completely cover the area outlined by my tool. I have reset brush settings as well as reloaded the brushes themselves. Notice in my animated gif that there is an area just inside the tool outline that is not covered when I click - even though hardness, opacity and flow are set to maximum and spacing is set to 1%. The area of the uncovered space increases proportionately as I increase the brush/eraser size.
EDIT: Brush size is set to normal and jitter is set to 0%