Line Chart Tooltip - X Axis Label

Hello,

I have a line chart that shows averages for 2 groups, the X-axis has three levels: Month, Week, and Date. (Figure 1)  When you drill down to the next levels of the hierarchy, the tooltip doesn't show the X-axis label.  This gets a bit confusing when looking at the week and date displays (Figure 2).  I'd like to add the X-axis label to the tooltip (similar to the column chart tooltip) so it changes based on the level you are viewing (Figure 3). I've tried creating a custom tooltip, but it shows all three levels at all times (Month, Week, Date).  Is there any way to add the X-axis label to the tooltip?

Figure 1:

Figure 2:

Figure 3: