Multi-line chart - line starts when other line ends
I'm attempting to create a multi-line chart that has one line that goes from the start date of a project until the last date a cost was recorded for a specific type of cost of the project, accumulating along the way. The second line I would like to start at the end of the previous line and continue until the end of the project, also accumulating, based on a different type of cost. I've attached a sample application with the chart I have so far and what I have for my data model. I've worked out how the first line works but can't seem to nail down the second line to get it to do what I want (it's almost doing the opposite of what I would expect, regardless of the direction of my expression). Any help with the expression for the second line would be appreciated!