Hi - I've figured it out - turns out it was a problem with my code.
Just for reference, what I was trying to do (and did) was to find a way to set the height and width of the chart-area minus the labels so that they all share a similar width, date-point size (e.g. bar height) (and scale) BETWEEN the charts.
So what I have done is
1) Set the scale for all similar charts to be the same (as per normal method)
2) calculate max label length (character count) and multiply by 5 (since 1 character is about 5 pixels wide)
3) Add a fixed size to the label-pixel count (e.g. 300) which becomes the width of the chart-area (excluding labels)
4) calculated the number of data-points for the chart, multiplied by 20 (so each data point is about 20 pixels in size for a bar chart)
5) Add a fixed amount to cover the header and footer of the chart. For a bar chart, 60 pixels seemed a good amount.
I calculated those values and then use the variables in place of the hard coded numbers...and it seems to have done the trick...it is just a bit code-heavy when it would be nice to set these sizes directly :-)
The reason for doing this is that for usability purposes, having multiple graphs of the same type having the same dimensions of the graph and data-points makes them easier to read and compare.