Camera angle has a real, measurable effect on transformation quality — extreme angles genuinely make the model's job harder, while a few reasonable options all work well.
Straight-on and slight angles both work well
A fully frontal shot or a modest three-quarter angle both give the model enough facial data to work with reliably — neither is dramatically better than the other for most models.
Extreme angles lose information
A steep upward or downward angle, or a near-profile shot, hides a meaningful portion of the face's actual structure — the model has less real data to preserve, which can produce a less accurate or less recognizable result.
Distance matters alongside angle
A photo where the face takes up a reasonable portion of the frame (not a tiny face in a huge wide shot) gives the model more actual facial pixel detail to work with, which compounds with angle to affect final quality.
Is a full-body photo or a close-up headshot better for a face-preservation app?
For apps focused specifically on facial likeness, a closer shot where the face is clearly detailed tends to work better than a distant full-body photo where the face occupies only a small portion of the frame.