9W is quite a low amount of light for HC. They do need quite a bit of light to grow and spread well.
The CO2 for me is more important than the lighting. There are members here who have grown R. macrandra with only .9WPG, but their CO2 levels were high and stable. Tom Barr, I haven't checked the Barr report in ages, but he had this to say about PAR lighting levels in ADA tanks. HC is mentioned as one of the plants.
http

/www.barrreport.com/showthread.php/4902-ADA-lighting-at-Aqua-Forest-and-nice-low-PAr-values-who-knew
I don't normally link to forums, but I think the research is quite interesting. In my personal experience, I find HC to want more CO2 and nutrients rather than lighting, but it could just be me. Normally, however, when there is more lighting, the hobbiest tends to pay attention more to maintaining higher CO2 and nutrient levels, so the HC gets what it wants anyways. In lower light levels, this is not always the case. I have grown it under 13W. Granted, it was pretty slow, but it grew. I was able to grow its larger cousin, HM, very successfully without CO2. I have little bits of HC even floating around in my .77WPG bowfront. The little bits are still quite alive.
Many here have also dry-started their HC by growing it emersed.
llj