It does seem a bit unpredictable what will work with automation and personally I would go with 1/3 overlap at least shooting wider.
You do have the advantage as well that you get a final image with fewer abnormally shaped edges as well.
There are a number of reasons that this particular Pan was difficult to stitch. However the 28mm wide angle equivalent lens was not one of them as the focal length makes no difference to the difficulty of pan stitching.
The real difficulty is that 90% + of the overlap area is either sky or water, which is not suitable for placing and defining control points either automatically or manually.
the actual size of the overlap was no problem at all. in most circumstances 10% to 30% is perfectly satisfactory, especially if there is suitable static detail to select from.
Of course, unlike stitching programs based on PTTools, we have no Idea how Photoshop or Lightroom actually work as the details are not published. however we do know that in both the seams are set to run down the edges of features. ( you can see these in the masks it produces). so if there are no features it is somewhat hit and miss.
PTTools on the other hand works entirely differently. as it first creates images shaped to fit on a sphere, using the the equivalent focal length of the lens. it does this in part by matching control points on each pair of joins. These can then be slid around the sphere till they overlap and orientate. This now spherical surface is then plotted using the chosen projection to produce a flat images of each exposure. ( the shape and orientation of them can be seen in my post #8 above.) these are then blended to avoid parallax and colour and tonal differences into the final output.
The shape of the edges is defined by the Projection chosen.
Software based on PTTools can make perfectly stitched pans from a mix of images taken from the same viewpoint, even if the focal length , focus, or camera orientation is changed between shots. provided that they all overlap. With large skies it can be advantageous to use a wider focal setting for the sky, so that you get sufficient overlap with the ground, and a longer setting for the landscape detail. The reason being you can not set control points on the sky.
Even when a pan can be done automatically it is best to check where the control points are in case they have been placed on moving objects like people, animals, cars, leaves, sky or water.
as such points can result in strange and unacceptable stitches. (Unfortunately there is no way to check this in Adobe and some other auto programs.)