For a good cover, you should use STRONG light. and your tank being 23" tall, you might want to consider a T5 HO fixture, or MH. For ground cover like HC, it is best to use a fine powder over the coarser clay where you plant it so it's tiny roots can develop.
Of course you can do MOSS groundcover and it can handle the lower light, so it depends if you want to adjust your lighting to the plants you want to grow or if you want to pick plants that will grow with what you have. Many LIGHT LOVING plants, ground cover, foreground, or mid ground will tend to grow TALL and LEGGY (thin and far between leaf nodes, not very attractive) when in light conditions that are not strong enough for them, they are trying to get up to the light level they desire. IF you provide them with strong light to reach them down far enough, then they will carpet and thicken up and look like they do in the tanks you first saw that made you want to grow them.
Of course you can do MOSS groundcover and it can handle the lower light, so it depends if you want to adjust your lighting to the plants you want to grow or if you want to pick plants that will grow with what you have. Many LIGHT LOVING plants, ground cover, foreground, or mid ground will tend to grow TALL and LEGGY (thin and far between leaf nodes, not very attractive) when in light conditions that are not strong enough for them, they are trying to get up to the light level they desire. IF you provide them with strong light to reach them down far enough, then they will carpet and thicken up and look like they do in the tanks you first saw that made you want to grow them.