I see. In my opinion the A/F ratio is correct when you set it at 270F. Just because the heat sink is smaller so the temp is a little higher. We all use 11fins bigger heat sink,so our temp is 20C cooler. As long as your engine will not go out and works fine each tank. A little hotter still ok.

Also I tell you one thing,most of the thermometers on the market are not precise. Except you use high price temp gun(more than $200US?!). I have tested many thermometers,all of them have huge different results. Sometime even more than 20C different. I don't know which one is correct so I use "Exagen" now.