A 32-year-old woman with primary infertility for 3 years undergoes diagnostic laparoscopy. She has regular 28-day cycles with normal luteal phase progesterone levels. Laparoscopy reveals multiple chocolate cysts on the ovaries and dense adhesions in the pelvis. Her sister, also infertile, has a normal laparoscopy but hysterosalpingography shows a rigid, non-patent uterine cavity with a single cavity on ultrasound. Which single feature best distinguishes endometriosis from uterine factor infertility in these two cases?