The name of the series
The height of the header and neuron ID text
The category axis for determining the y-value of the tooltip
The tooltip style
The plot margin
The height (in pixels) of the category
The dimensions of the plot
The y-coordinate of the lower-left-hand corner of the tooltip rectangle
Calculates the y-coordinate for the upper-left-hand the tooltip rectangle. Adjusts the y-coordinate so that the tooltip is visible on the upper and lower edges of the plot