If you have 14 TCH TS you have 8.2Erl at 2% blocking if you enable HR or AMR-HR then you have 28 TCH TS which gives you 20.15 Erl at 2% blocking. It is interesting which value to use if you AMR penetration is not high enough. You can see the penetration from different phones used in your network, i think IMEISV from MSC/billing guys. We always use FR capacity for offered traffic and have in some places utilisation over 100%.