and the pistons, and then rings, and the valves, and anything else near there...
As Iceberg has told me again today it must be something to do with it being the first cylinder to get nice clean air and lots of it and last on the injector rail. Now this isnt a problem for me most of the time on LPG as the 5th is the first on the rail of LPG injectors. I can see one way around it being to feed the injecto rail from both ends