For each axis, the TextLabGap value gives the spacing between the descriptive label and the edge of a box enclosing all other parts of the annotated grid (excluding other descriptive labels). The gap is measured to the nearest edge of the label (i.e. the top or the bottom). Positive values cause the descriptive label to be placed outside the bounding box, while negative values cause it to be placed inside.
The TextLabGap value should be given as a fraction of the minimum
dimension of the plotting area, the default value being 0.01.