Basically if you can fly direct on BA from DTW to CMN on a one flight number direct BA flight, then you only pay the 60K award. But unfortunately you have to fly via LHR and the miles on the connecting flight is calculated.

So you would have to fly DTW-LHR-CMN even if you have no intention of stopping in LHR. Your award would therefore be the 5050 mile award = 100K miles.