Imagine the description of morning in the last but one post is the start of a novel, part of a 'fictional world'. What this means, firstly, is that you have detached the description from a referent. It is not longer a description of an actual morning, an actual cafe, a specific time and place etc. The 'steps' and 'doors' and 'trays' no longer refer to those experienced by an individual in real life.
What difference would it make to the reader? It seems to me that you would be more likely to see it as a metaphorical vehicle as well as a description of a place. You would be more likely to see it as an evokation of possibility as well as a description of a city morning. As soon as you jettison the real-world referent, the metaphorical content becomes visible.
We can perform a reverse thought experiment with a fictional work, for example Elizabeth Bowen's Last September. Elizabeth Bowen produces a whole poetics of space in which the merest descriptive detail has a dual life as a metaphoric vehicle and marker of some larger class-consciousness. The great high windows of the Irish Big House at once suggest Enlightenment, the cool eye of the aristocrat, yet are typically curtainless, subject to incursion from without. The demesne is well cultivated, walled and enclosed, embodying certain enduring values of privacy and order. But this security and closure contrasts embarrassingly with the impoverished open landscape of the peasantry and tenant farmers outside the gates, heightening the sense of alienation. All around the demesne, in Bowen's Last September, the "orange bright sky crept and smouldered", like some coming revolution. The Big House became the focal metaphor of an Irish Proetestant Ascendancy increasingly menaced by the empowerment of Catholic Ireland.
Now if we read such descriptions of curtainless windows and smouldering skies in her letters or autobiography, we are less likely to see a metaphorical outline. They are too anchored to a real person and a real time. It is by freeing description from actual space and time that the metaphoric outline emerges.
And by contrast, you are always more likely, when reading descriptions of objects and situations in a novel to perceive, or be at least dimly conscious of a metaphorical outline. In other worlds this outline becomes visible when you've jettisoned any real-world referent. It becomes available for metaphor.
But my point is that fiction does not impose this metaphorical outline, by a kind of decree. The 'metaphorical outline' must be there to begin with, silently or implicitely, in the beginning, when still anchored to a real-world referent. Fiction simply undoes the anchor, releases it, brings it to visibility.
Things already have a metaphorical outline embedded in them.