This is a rather clunky suggestion without much flexibility, but I tested it on your sample data and it seems to work.
I created this new formula:
And added to the chart area, you need to add [Email Address] to the Month to Month Dropoffs mark card as a detail.
Also use dual axis and synchronize axis.
In this approach only the bar graph works for me and the label marks would not populate correctly. I am sure there is a better solution, but I can't quite reason it out.
Sample Email Clicks.twbx 35.6 KB
Thank you! That seems to be working!