One 45 inch reflected umbrella, fabric at 40 inches (a distance not exceeding the umbrella diameter).

Almost as good, and 18 inches is not always practical. The greater distance fills less well than if it were closer, the shadows are slightly darker, but the difference is subtle. The umbrella shaft does prevent it being as close as shoot-through can be, but reflected is a wider light for larger subjects. Close as possible still applies, and the "diameter" is a typical close distance for portraits - the sitting subject typically can reach out and touch the light stand pole of the main light (not the fill however, it has to be more back with the camera to be out the way of the lens).