Increase mouse-over area of points on a line chart for tooltips

[Alex Topiler]

The mouse-over area to trigger tooltips on a charge seems to be set to a small circle surrounding each point on a chart (i.e. a line chart).  This causes tooltips to only show when you hover directly over a point, instead of always showing a tip for whatever the closest point is.  I noticed that the behavior for tips when using the 

focusTarget: 'category'

option actually shows the tips of the closest set of points at all times.  However, this option doesn't work for my use-case.  Is there any way to get individual tooltips to behave in a similar way where tooltips will always show for the closest point when hovering over anywhere on a chart?