What do you mean by daily range? (High-Low)?
ATR is the average true range for the last n periods. The true range however, is not the High-Low for every day. True range is the maximum value of the following 3:

1.CurrentHigh-CurrentLow
2.Abs(PreviousClose-CurrentHigh)
3.Abs(PreviousClose-CurrentLow)

I hope you understand. Now, please tell me what exactly do you mean by the average daily range.

Bye.