Photoshop Devs: I'm currently using an AI tool called Expression Editor [link removed by moderator] which is based off an open-source AI technology called Live Portrait.
In my line of work facial expressions need to be nuanced. Eyebrows, corners of lips, teeth, pupil direction, hand direction, and many more subtle facial details are critical. Currently your Smart Portrait filter is not powerful enough to do all these thing so I use Expression Editor and bring the output back into my file.
Please consider mimicing their features. Perhaps consider embellishing with other neck movements (e.g. crane, lean back). I like how they use sliders for all their attributes so the exact expression can be dialed in.