A character can be considered large in fiction if their size has a significant impact on the plot. For instance, King Kong is not only physically large but his size is what causes all the chaos and adventure in the story. His huge form is what makes him a threat to the city and the people in it, and also what makes his capture and transportation such a complex and dangerous task. So, it's not just about physical dimensions but how those dimensions play into the narrative.
Another factor could be symbolic size. A character like the Great and Terrible Oz from 'The Wonderful Wizard of Oz' may not be physically huge like a giant, but his power and influence in the Land of Oz are so vast that he can be seen as a 'large' character. His commands are far - reaching, and his presence is felt throughout the land, much like a large physical entity would be. So, in fiction, 'large' can also mean having a great deal of power, influence or significance within the fictional world.
Size relative to the setting. For example, in a story about a normal human town, a giant like the one in 'Jack and the Beanstalk' would be considered a large character because he stands out so much compared to the normal - sized humans. His huge height and mass make him a dominant figure in that fictional space.