Croceas want a solid surface to attach to, so they can live on the sand provided that there's enough light and they have something solid under them.
If it were me in this situation, I would pick a light for the animals I want to keep, adding several fixtures can look a little funky, but that's personal taste. I would pick a light that can replicate a nice "daylight" spectrum for at least the peak hours of the day and you can "blue" it up for the ramp up/down. I would much rather have a light that I'm only using 50% of it's power than max out a light that barely has enough power. If you want to keep a clam, especially crocea or maxima, you need a light that can provide them with everything they need. Look for a used Kessil 360x, it would light your nano and has a great spectrum. But you can also find nice powerful fixtures on Amazon, Aliexpress, etc...if you want to keep a clam, the only thing that really matters is the light, it's what drives them and provides everything they need. I would look for a slightly bigger fixture and simply reduce the power.