I concur with Ken that air-layering is the best way to propagate FLFs.
How big is the top section you are trying to propagate? Can you post a photo that shows its size?
The primary problem with propagating by cuttings is that the large leaves tend to dehydrate before roots get a chance to develop and supply them with the water they require. Keep the cutting in damp potting mix and the pot and plant inside a large, clear plastic bag that you blow up and then seal. This plastic tent will maintain the moisture in the soil and in the surrounding air and give the roots a chance to develop. If you do this, make sure that you give it lots of bright indirect light, but no direct sun that will cause the interior to overheat and "cook" the plant. This is a bit unwieldy but can greatly enhance your chances of successful propagation of the top cutting.
