Let's start with a panoramic image:
Select number 1 in the curve Segments list.
Add the first horizontal curve and set it like in the image below:
Select number 5 in the curve Segments list. The image should look:
Select number 1 in the curve Segments list. Add a new horizontal curve like in the image below:
Set the curve to the curvature like in this picture:
The curve is recalculated to 2 curve Segments for precise setting. Press the button "Straighten". The result should be like this:
There is no need for Ratio Adjustment.