rossghanim not sure how you have things setup (LAN, WAN, Uplink, etc...) but we are an ISP, and we only have netflow enabled on our 2 core asr-9k uplink interfaces.
After we enabled netflow on those 2 interfaces, I went into NTA settings and added IP Groups.
i.e.
Group A: 10.0.0.0 - 10.255.255.255
Group B: 172.16.0.0 - 172.31.255.255
Group C: 192.168.0.0 - 192.168.255.255
etc...
break them up however you like, or you can even do single IPs. (at least I think you can)
I have our different service areas setup into different groups, which allows us to see which area are doing the most traffic, and also gives us a better idea of future growth and expansion... and all that boring number stuff...
Hope it helps... at least until a better answer comes through...