Hi Jon,
Just wandered over here, haven't here in a while. Downloaded your
sample addin and did a quick test. I'm getting inconsistent results.
Mostly correct. Occasionally not, then correct again.

two column 2d charts with data

red 1
white 2
blue 3


red 300
white 400
blue 500

change plot area in 2nd chart to smaller
change font in second chart to 18 point

resize everything. Inside left axes are identical, good
Inside plotarea widths are usually the same which is good. Sometimes
not the same. But almost always the Inside plot area positions are
different relative to the chart area which would be nice when using
these are sequential pages in PPT.

Brian Reilly, PowerPoint MVP