Trigger words: "CHR, sphere head"
Additional tags:
"brown eyes" (basically any color). If this tag isn't used images will have bad eyes.
Tag "red skin" isn't really needed, but you can add it if you have troubles with coloring.
Put tag "empty eyes" in negative prompt to avoid them, or don't if you want.
Strength: 1 works perfectly. Lowering strength can slightly help with flexibility, but lowering below 0.8 results in appearance of artifacts and general quality loss.
Preferred settings: cfg = 5 or lower, steps = 20 or more.
Models to try: WAI-illustrious-SDXL (better use 14th version), HomoSimile (4th version), YiffyMix