Hi Gav, thanks for the feedback on the manual. We have tried to make it as informative and easy to understand as possible.
In answer to your question, I designed the heat pipe to be offset so the heat pipe and the heat transfer fin are at the top of the tube as close as possible to where the sunlight is contacting in order to maximise efficiency. This design also allows us to have a high tensile metal clip which supports the heat pipe and aluminium fin to ensure they remain tight in contact with the glass. Previously we also had the centralised heat pipe with a pair of fins but the aluminium looses its "spring" over time with the high temperatures, resulting in poor contact with both the glass wall and the heat pipe resulting in decreased heat transfer.
I have some ideas on improving winter production using a reflector board. I know the WAF will be low but it will only be up for a month.... 
Mid element tanks should be banned , they should all be twin element one high and one low , I know ET's are the best for heat generation thats a given but in the winter time depending on location a SWH struggles to heat 300 liters to 60c for a family of 4 or 5 and only has 130 -150 liters above the mid element which is not enough and more times than enough the family continually run out of hot water in the winter time...but hey they got maybe $100 or more in Recs value to compensate them...I doubt it they think of that in winter when they have run out of water and the kids are moaning no hot water.