Thanks everyone - admittedly I'm only up to post 104 of the thread so far so I realise I'm jumping ahead by asking for help without finishing my pre-reading first - but along with the limit of 6, I'm getting pricing errors.
Haven't completely finalised it yet but I'm looking at PER-xSYD-(1)HND/ss/KIX-xHKG-(2)LAX-xDFW-(3)IAH-xDFW-JFK-(4)HEL-xLHR-(5)BHD/ss/DUB-xDOH-PER. QF/QF/Surface/CX/CX/AA/AA/AA/AY/AY/BA/Surface/QR/QR.
GCM says 54,721km including surface segments.
I was hoping for JL but despite finding availability on both BA and JL websites, QF call centre couldn't see any of it (I called up just wanting to check the taxes).
Ah. Get you now. I swear I was able to trick it in to doing more segments than that previously but just tried and it didn't work. This might explain my errors...
Edit: Managed to break it again:
View attachment 87377