Sounds like she recorded the chorus multiple times. One center, one 50% left, and one right 50%. I can hear a higher pitched vocal very subtle behind the main chorus, seems to be panned the same way as lead chorus just a lot lower in volume. Have a play around with it and see what you can come up with. Just keep in mind that the tighter you can get the takes - the better it'll sound. << This is my obersvation on the Iggy one.
T.I one is most likely the same but with a lower pitch vocal underneath - from quickly listening to it anyway - again just try experimenting in different ways of recording it, be it distance from mic or tone in which you say it, but keeping the timing tight. Having a difference to the main vocal but having it panned out also will create an effect where the wideness of it stands out a little more.
Hope this helps, makes sense.
