According to the OP, I sense they were still seated in F for the short journey from ORD-DTW. If that was the case, the mileage refund should only be applied to the BCN-ORD journey and not the entire trip. While mileage totals are for the entire journey, miles booked are still segmented (ie bcn-ord could equal 110,000 and ord-dtw could equal 20,000 per person) just like a regular cash fare. So the roughly 133,000 miles returned would be roughly accurate for the 75% refund for that segment alone.

That being said, having glanced at EU261, it's not entirely clear if it means the entire length of the journey or if it's just by segment. Chances are since one of the flights completed happened outside of the EU, you are only entitled to the flight that departed the EU and not the entire route of flight.