If you have the territory to america,
you get sunday as 1
if you have the territory to spain
you get sunday as 7
To solve this problem you can create a trigger on logon to set the territory.
CREATE OR REPLACE TRIGGER TGR_SET_REGIONAL
AFTER
LOGON
ON DATABASE
BEGIN
execute immediate 'ALTER SESSION SET NLS_TERRITORY=''AMERICA''';
END;
/