You want something like this?
I don't think that you can set the position of the dimension label as property, but you can
a) disable the label in dimension tab
b) create a text in chart in presentation tab, entering the dimension label as text
c) resize you bar chart area and reposition your text in chart box using CTRL-SHIFT on the chart object
Hope this helps,
You can add your own title below the anywher in the bar chart using the
chart Properties --> Presentation --> text in chart --> Click Add button and add your own text inside the chart.
Then pressing the keyboard button ctrl + shift same time and you can move/change your text or bars width
Here you can move your own text below your axes values.