I have given some thought to the hairgrass position. So in accordance with my original plan (and other's suggestion) have moved a few hairgrass plants, spread strategically across the mid to foreground and around the stones. It's not easy to see in the photo but I think it looks better and anticipate the end result being quite effective. Long-term sustainability will be interesting but by then I'll be eager to try out new aquascaping ideas I'm sure.
Growth is good, the HC is spreading already with surprisingly little die-off. I imagined as it was grown emersed then it would suffer a little adapting to its submersed existence. Maybe it's too early to say. The hairgrass is also sending out runners too.
Anyway, here's a photo
Note the new background. I bought a cold-cathode all-in-one unit from my local DIY shop for about £10. It spans the length of the tank exactly and gives a white/blue hue. I've simply placed some white card behind the lamp and tank. As you can see the cathode lamp is low output so for "final photo shoots" I will upgrade to fluorescent. It is fun experimenting!