Question on using Warp Stabilizer on nested sequences

Hi,

If I have a 1920x1080p sequence, where in which I nested a 3840x2160 video clip that became automatically a 1920x1080p nested sequences, when I'll be using Warp Stabilizer on that nested sequence, the results will ne zooming on the 1080p nested sequence or on the 2160p original file ?

If it zooms on the 1080p it's gonna loose quality right ? How to avoid that ?