The definition of proportion indicates that things to cats are

equal or balanced in relationship to each other. In the context of cats, this means that there is a harmonious or balanced correspondence between various aspects or characteristics related to cats. It could refer to the size or dimensions of different body parts in relation to the cat's overall body size, the ratio of various traits or features such as the lengths of legs, ears, or tail, or the correlation between different attributes such as a cat's weight and height. In essence, proportion in relation to cats signifies a sense of balanced or harmonious aesthetic appeal in the physical attributes and characteristics of a cat.