The phenomena that affect perception are varied. An element isolated not look the same if you are surrounded by other elements. Its color, their size or shape are altered in the process of recognition to which our senses undergo.
A set of basic rules collected as “Leyes de la Gestalt” allow us to understand the processes that influence the shape recognition.
The Gestalt laws are based on the idea that "the whole is more than the sum of its parts”, outlining key elementary processes of the organization of information in the perceptual process.
The influence of the environment is one of the aspects that strongly influence the perception of size, as we can see in this instructional video that I found in the channel Richard Wiseman.