I’m having problems creating this plot so that all the 4 components have the right proportions. I would like to rotate the diagonal line (in the right corner) in a specific way so that it is exactly placed diagonally at the same height as the trendline of the basis plot with the two conditions x1 and x2. In other words, the dashed line of the upper right “plot” is supposed to continue the trendline of the basis plot. Then when I enlarge or minimize the plot, it shouldn’t lose these proportions.

enter image description here -> how the plot currently looks like
enter image description here ->how it should look like