Final answer:
For a fetus in the ROP position, fetal heart tones are best auscultated below the umbilicus on the right side as this is where the fetal back is closest to the maternal abdomen.
Step-by-step explanation:
When the fetus is determined to be in the Right Occiput Posterior (ROP) position following a Leopold's maneuver, the best location to auscultate fetal heart tones using a Doppler would be: below the umbilicus on the right side. This is because in the ROP position, the back of the fetus is lying toward the right side of the mother’s uterus, which is generally where the fetal heart tones can be most clearly heard. While performing the auscultation, it's important to position the Doppler in the area where the fetal back is nearest to the maternal abdomen to optimize the reception of heart sounds.