If you want use this particular HDRI, then i would recommend a different Environment Dome than EnviroBoxSharp or any of those standard domes. There is a Sphere with inverted normals named “Sphere_inversenormals” (it´s part of the Engine content, so you have to make that visible first), take that as Environment dome, and those deformations are gone. With that sphere, it is almost like camera projection, but you can move around and see position change in your HDRI. And because it is an actual sphere, and not just a half of a sphere like the normal dome, you can set the projection center to zero.
How to find this Sphere_InverseNormals dome and how it will look with the HDRI Backdrop:
Nah, it´s a combination of an unlucky HDRI texture and dome, i think, this HDRI would not work well with any standard dome, as it is made from a very small room, that would not allow much movement without distortions. I guess, there is such a thing as a minimum size for real life places, that needs to be uphold to work well with HDRI backdrops. And the original shop/room seems to be way to small/below that limit.
And that resolution you mention, you cannot go higher than the latter number/height of the cubemap texture in your max ingame resolution 
so you want to be as close as possible to the height of the cubemap. With that texture, even if you set the slider to 4k, it will stay at 2048, but it´s not a problem, it still uses all of the texture at full resolution.