How to switch expression generated line sections in QGIS?

Question

According to this thread about "Changing length of Shortest_Line for CAD-like slope pattern using QGIS" (https://gis.stackexchange.com/a/386104/212966) I would like to learn how to switch that generated pattern to start at the end point.

I understood that the red line is the result of a connection between two points (one startpoint, generated with that referenced tool "points along geometry" on the upper line and one endpoint, retrieved from the intersection of an virtuell line from the startpoint to the nearest point on the lower line) thats length is controlled by a parameter (in that case .50, see 7th last line).

Conceptually conditioned that example of expression generated pattern creates best resultes if the baseline for the interpolated points is the longest line of the upper or lower line (see example in the thread). As in civil engineering tasks the upper slope rim isn't always associated to the longest line it would be helpful to switch the generated line segments (red) from startpoint -> middle to middle -> endpoint

(or in other words: I would like to have the first half of the line "transparent" and the second half as generated pattern.

Using the shortest line as baseline (in that case labelled as "lower") is surely an option but it does crush that actually nice pattern.

Answer 1

By figuring out how to use reverse(geometry) I found one other appraoch:

As in line 23 make_line is used with a startpoint ($geometry) and a projected targetpoint (project) changing $geometry to @varinter in line 24 will return the inverted pattern.