Hi Geoff,
Our 160 seems to use fuel from the port tank first and then the starboard, at first I was a bit concerned but I did a few close circuits when I had about 10 litres in the port tank and about 50 litres in the starboard tank as a test, when I returned I still had about 10 litres in the port tank and the starboard tank had reduced its level. I have run my fuel lines very similar to how you have done yours and I can't see any viable reason for using more fuel from one side more than the other, all I do is make sure my total fuel for my trip is enough and just keep an eye on both levels, and as long as I can see fuel in both tanks I do not worry about it too much. I have also parked my plane on uneven ground, and by doing this I can move fuel from one tank to the other just by gravity, it works both ways so I am confident that the way that the fuel feeds to the header tank is ok.
All the best
Brian