Polar and spherical panos are two different images. A polar pano image is almost like a snow globe. The image is basically turned inside out. For an example, the ground becomes the frame around the globe and, the sky and objects smashed inside the frame. A spherical pano is when a scenery becomes it's own miniature world. The ground becomes the world while the sky is surrounding it.
The one thing that makes my tiny world convincing I the way I edited it. I made sure all the colors matched each other so it wouldn't look like a line was going through my world. Another thing that made it convincing is that I made hopefully everything even. For an example, I had to even out the shape of the water in my sphere world.