Adding WS to a nest clip is a pita: takes ages to stabilize.
IMO it makes no difference if WS is applied to the clip or to the nest regarding amount of cropping
The higher the (additional scale), the more image quality loss it will suffer for clips with the same resolution as the sequence or nests.
If the clip still crops, you will have to accept the clip is not suited for stabilization - as in too much motion.
Premiere can do wonders: it cannot perform miracles.
WS is meant for handheld footage.
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