Thanks mattmos! You've got sharp eyes, I think you're the first to notice the lighting angles are a little bit off. I think I'll live with it though. The shadow is essential as an indicator of how high (or low) the aircraft is and I like it's placement. The angle is also ideal for the key light on the aircraft. When I shot the reference photo I used for the background the sun was actually higher than it may seem so it's not too far off. I really like the look of the sky which is hugely important. In this case I think the artistic look is more important that absolute accuracy on the light angle. Thanks for pointing it out though.
The grass (new crop in the field, probably not actually grass) is thinner on the edge on purpose (weight map). It's on the other side of the fence near a road and also wanted a clear place for the pilot signatures at the bottom. I guess I should check the average color of farm soil in France! I'm just going by what a field looks like here but that might be very wrong
PS - I should mention I'm using the very handy Zybrand grass, I love it!
Edit: Looks like my dirt color is off for typical France (at least the references I can find). Damn! Should have thought of that sooner...