Okay, I see what you mean. It doesn't seem to be anything shader-side - I can only get the weird behavior just after startup, as soon as I re-center the view even once (mouse right-click) it's all back to normal. So this must have to do with the way the cockpit view is initialized, which gets the view manager to transmit weird offsets, and once this behavior is reset it's fine again.
I guess directly writing into <current-view> from aircraft-set is something you should just not do (or do right, not sure whether this would work) - this is what seems to create the inconsistent state.
The cone is so big in size that it cannot come out the front canopy without illuminating parts of the canopy.
There's really no cone - it's just a circle drawn in screen coordinates. It can't be expected to know that your plane is your plane unless you tell it. There is a distance cut to get rid of the worst effects on the panel, but the recommended procedure is to use model-interior to render the inside of the plane (which comes with your set of lightmaps, grain overlays, shadows etc.) and you won't see any light on that ever (it's also faster because it never does any fog computations).