Planet in its own nakshatra — effective lord becomes the sign lord of that sign
Mutual star exchange between planet and its star lord — use sign lord of star lord's sign
Planet in own sign or exalted — keep original star lord as effective lord
2+ planets in this planet's nakshatras — keep original star lord (ambiguity)
Exactly 1 planet in this planet's nakshatras — that planet becomes the effective lord (unless debilitated)
