In 1.8, skulls were rotated and scaled correctly in first person. In 1.9, they have default scaling and rotation in their model leaving them looking odd.
When I went to change it in my resource pack, I noticed that there wasn't even a section for first person in the json file, so not sure if it's intentional or just forgot to add one
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[media]

Duplicate of MC-91869. Please attach your models there.