Sometimes you have to use your common sense - I recently had to fly LON-WAW-LON. Cheapest two *A options were:
a) LHR-MUC-WAW-MUC-LHR on Lufthansa (J) for approx. £410
b) LHR-FRA-WAW-FRA-LHR on Lufthansa (J) for approx. £430
Even flying via MUC would only net just over 4,000 status/destination miles, and I didn't think it was worth paying over £400 for that. I considered flying LH in economy then to save money, but...
What did I choose in the end?

c) LTN-WAW-LTN on Easyjet for £25 return inc. tax
OK, service was crap but it was only a short flight and the £380 difference was used towards my new widescreen TV
I'd go with EK if it saves you the miles - they can be much better used on a different route. That £1681 really is a bargain so book as soon as you can!