Values an axis - textAngle

Hi pentaho-family,
do you know how we can make extension points for bar chart depending on number of values that need to be shown? I'm using xAxisLabel_textAngle, but sometimes I have 5 bars and sometimes 25. It would be nice when angle can be set depending on number - e.g if I have ranges - {<5 bars, 15, >15} can be xAxisLabel_textAngle = {-1; -0,7; -0,3}.

Thanks a lot for any ideas.
timfu83