Perspective has nothing to do with focal length. The reason wide angle lenses show more perspective distortion than longer lenses is that you're standing closer to the subject. That's it. Crop a 20mm shot 10x and compare wit the same image shot FROM THE SAME PLACE with a 200mm. Perspective is identical.
2. A crop sensor body does not turn a 200mm lens into a 300mm lens, and crop sensor bodies do not "stretch" faces out less. The reason you might think this is true is that you're generally standing farther away with a crop body than a FF body (see point 1).
So repeat after me: focal length does not affect perspective. At all. Ever.
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