ETC Source derivation for Forecast generation at Project Level

Hi,
In PJT (Oracle Project Management) , i am trying to generate the forecast through "Generate Forecast". The forecast is at project level.
As of the Oracle user guide , if in generation options if the source is Task Level selection , then ETC is derived from Task Setup.
But if the forecast is @ project level then where to configure the ETC source?
I generated the forecast line (project level) when edit forecast line , the ETC source is null .

Any idea on this?

Cheers