We have a page with many spark lines, for example:

As the user hovers over the chart we have a toot tip display as you can see in the example above.  The user can click any of the charts at the point that they want to drill into more detail.  For example, in the example above the user has moved the mouse over the Corrective Work Orders spark line and then to the 16th week of 2022.  The tooltip is telling the user there are 55 work orders in that week.

The problem: The click event is not always in line with the tool tip.  In the above example what actually loaded was the data for week 17 (not 16).  It's a very specific issue in that if you click in the top part of the chart it will always load correctly but if you click in the bottom 30% or so of the chart it seems quirky, sometimes it will load the correct week, sometimes the wrong one.  You can see in the diagram the mouse cursor is behind the highlighter line at week 17 (I've circled that line in red), but the tool tip shows week 16.  We could tell users "make sure you click in a perfectly vertical line to the highlighter line" but users do what user do and will expect the tooltip to be accurate to the detail they see when they click.  The problem with this we give the wrong information and something bad happens.  I tried setting absolute heights and widths because it was previously even worse and this got me to the 70% right vs 30% wrong situation I have now but I'd like to fix it.

Has anyone run into this previously and found a solution?  Can anyone recommend any course of action to narrow down the issue further?