What I've seen is...
One pack+1 eng 440kg/h eng + APU burn. Open crossbleed FF then goes 480-500kg/h+APU burn, with a much higher Idle (IAE when both pack selected on)
Mode I like is, 1 eng, 1 pack (other turned off) crossbleed open so the eng start procedure takes 10sec rather than the 30sec when you have to wait for the crossbleed to open (more looking out time!). As you have the second pack off the idle doesn't modulate higher.