I wonder if this system is connected with wired ethernet or wifi. I found that it makes a large difference on my NAS. With a wired link the SoC can't reach a deep sleep state because the ethernet peripheral demands low-latency wakeup from the PCIe root port. This is power management policy that is flowing from the link peer all the way to your CPU! I found that wifi doesn't have this problem, and gives better-than-gigabit performance, sometimes.
If you have an network card over PCIe then there may be an issue with the card. I have never had an issue reaching low sleep state, you can modify WoL behaviour too. Wifi is, again in my experience, uses significantly more power. I have seen 3-5W and usually switch if off.
I don't think it's an issue with the card. It's a combination of ethernet and PCIe features that make this happen. There is a standard called "energy efficient ethernet" that makes it not happen, but my switch doesn't do it.
