Merged cells in table causing gaps between chart axis labels

[OmniBlue]

Please see the attached table and associated chart. Note that I created this simplified example for the sake of clarity--The resulting problems in my actual charts are more pronounced--gaps causing horizontal axis labels to wrap, etc.

The 2013 and 2014 column headers in the table (which are in merged cells) are causing a gap between the 2013 and 2014 horizontal axis labels in the chart. When I select the chart and then go to "Select Data" in order to investigate, I find that there is a blank line between the 2013 and 2014 entries within the Horizontal (Category) Axis Label section--presumably due to the merged cells. I'm unable to delete this blank line
(which I had hoped would remove the gap between 2013 and 2014 on the horizontal chart axis).

How can I select data for the chart such that the merged cells will not produce gaps along the horizontal axis?

Thank you!