The various levels you are seeing are called LOD's (Level of Detail). This is highly influenced by the Video Options setting Object Quality. Each block model (not shapes) in the game has various LOD settings based on distance to the camera. In a recent code change to improve performance, these values were updated in code and now need to be updated on a per object basis. This will be WIP through various A20.x releases.
Also, this is a very old model that will be getting an update in A20.x or A21.