I've flown an intra-EU itinerary - NCL > LHR > VCE

NCL > LHR was delayed due a battery fault, causing us to miss our LHR > VCE connection, resulting in a late arrival and valid EU261 claim (ended up about 8 hours late arriving at VCE)

However in our claim we calculated the distance as the combined distance (using great circle) of LHR > LHR then LHR-VCE. This is over 1500km.

However the airline is claiming the distance should be calculated as LHR > VCE, which is a few km less than 1500km.

I've searched high and low and can't find an authoritative answer to how the distance should be calculated in this scenario (either way). I wouldn't want to accept less than we are due, but without a solid source to argue any other way, it looks like we'll be accepting the <1500km compensation.

Thanks in advance if anyone has an answer to this, SC