I think that with an 18" deep tank, you're going to have a tough time even with low light plants at the bottom of the tank. You might want to consider the Ray II. There should be a chart showing the PAR data for the fugeray and RAY II fixtures at specific depths on the finnex website and/or in the finnex / schuber wright forum on this site.
You might be okay with those plants, especially if you attach them to wood or stones so they sit above the substrate level, reducing the distance between the plants and the light. Just don't crank the CO2 and go nuts with fertilizer, because with such low lighting and such slow growing plants, they are not likely to use nutrients very quickly and you will just promote algae growth.