Have you tired making your bar-chart out of gantt marks?
Set up the bar-chart as you would normally, and change the marks to gantt. Then create a negative version of your measure, and place that on the size (this will take the gannt back to the zero axis for a single bar). If you have a stacked bar, you'll need to do a bit more math on the negative values so the stack, and don't over lap.
Like the way you've used reference lines to control the axis-range...in the absence of true dynamic control of Axis this is a trick I employ a lot.
Hope that makes sense, and helps...if not let me know.
Thank you very much for your suggestion. Unfortunately that did not work either. Because I can't use exactly the same 'type' of items, it's still sizing differently. When I put Measure Values, to get multiple items in one column, instead of one measure, it changes. Even if it does line up at one point, when changing dates, it goes out of sync.
That's a shame
...Are you able to post an anonymised version of your workbook (as a .twbx) here? as this kind of 'fine-tuning' is tricky without seeing the workbook. I assume you've explored, and then failed, to get the Viz onto a single sheet?
or even a screen-grab (redacted for any sensitive information) so I can see what is stacked and what are gannt marks, may help...workbook is obviously the best option, but if a screen-grab is all that's possible, can you indicate which stacked marks are dimension's that are stacked over a single measure and which are stacked measure names.