However, I then tried to create a similar ramp but with different length run offs, the same technique doesn’t work! How can I complete this corner so the curves of the ramp meet perfectly like in the top picture (image of problem is bottom image):
Make your ramp base a solid box, create a cylinder along one side so it overlaps at each end. Use the solid tools to subtract the cylinder from the box. Repeat for each edge.
Or else draw the ramp profile at the middle of an edge (cut out a little bit to allow this), follow me around the remainder of the edge, and then use pushpull to fill the gap. On occasion, followme doesn’t get the fact that you wanted to go around the corner, not stop there when the profile is located at the corner.
I misunderstood that detail of your post! Followme deals with only one profile at a time, so it is not possible to use it directly to join two different runoffs at the corner. What you need to do is to extend the edges past the corner and followme each runoff through where it crosses the other. Then use Intersect Faces With to generate the edges where the extrusions cross and finally erase the extra geometry past the intersection. Depending on the size of your model, you may have to scale up before doing the intersect to avoid issues with small edges.
The technique @justcheckinm8 suggests will work only with SketchUp Pro. You could construct the cylinders he shows and use Intersect Faces With to achieve the same basic idea in Make.
You can also start by creating an uniform shape, and then select one of the sides and use the Scale tool to stretch it. The profile will become elliptical, though.