especially through aux input , direct ipod control im not sure about but i dont think it does since your controlling all volumes through the HU so thats where HU clipping has to be factored in
Its all revealant to your other settings on your head unit and amp. So, IMO there is no correct answer. I have to run my ipod volume all the way up with the eq off on my head unit. I also noticed, there is quite a difference between generation ipods. Like I said, it depends on your setup. You should know when its distorting.