A further thought. I'm not sure if SYD-HKG-SIN-LHR is valid for your second Asia visit. You might need to do SYD-HKG-LHR, SYD-BKK-LHR or SYD-SIN-LHR. Hopefully someone else will be able to confirm whether this is a problem or not. If it is a problem, then perhaps do HKG-PEK-HKG-NRT-HKG to use your 4 segments in Asia, and then the direct through for your second visit. (Or use CTS instead of NRT, but frequency of flights is less, and no F).