Thanks to the persistant and knowledgeable efforts of IvanK, all mixture woes are now resolved for every model of Spitfire and Hurricane in this latest patch. It was a real goofup since the initial release back in 2011, but it's now all fixed.
In a nutshell, keep the mixture fully back in the Auto Rich position and forget about it. There are only two positions for mixture -- Auto Rich and Auto Lean. As in the real aircraft, the mixture control is mechanically linked to the throttle lever. You cannot shift the mixture lever into Auto Lean when the throttle lever is back. Auto Rich will give best performance at all altitudes and engine settings. Auto Lean is only used for level cruise at altitude at reduced boost and medium rpm setting for staying in the air on extended patrols to conserve fuel. In Cliffs of Dover, many 109 pilots are willing to relieve you of any worry of that kind.
Here's some additional info:
http://theairtacticalassaultgroup.co...(Merlin-engine)