This continues to be a genuinely interesting photography thread, as the focus is on ideas of composition, not just the normal editing/criteria/rejections. I was really looking forward to catching up on this thread today - that's a situation that has been all too rare recently on the Forum. So, once again, I want to congratulate all on this mature debate.
For me this is as much about motive as centring. I am in agreement with Mick again that a 'motivated' cropping is not what is being critiqued here - it is when a subject is placed particularly in the frame without any apparent positive merit. Thus, I would interpret A.net's criterion as saying that they want the subject to be centrally placed unless the motive of the image demands otherwise. I hate using other people's photos as examples so I will try to find something of my own....
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Photo © Paul Markman
Technically this is not centred, if you assume the whole formation is the subject - i.e. it is placed over to the right. However, I would argue that - as a photo - this is correctly composed, because the smoke trail, together with the formation shape, suggests a sense of movement from left to right, and thus the composition works - the 'movement' is part of the motive for the image. If I was forced to centre 'in the middle' there would be very little smoke, dead blue sky in front of the formation on the right, and that sense of 'travel' from left to right would be lost. That, to me, would be formulaeic centring. I am glad that this shot was accepted as it is.
So, going back to Juan's post (Reply 14) I see what he is saying about the amount of sky in my shot, but any negative with that is massively outweighed compositionally for me in that the subject - the whole plane - is centred. In my opinion, I cannot see any motive for Colin (sorry Colin for talking about what you were thinking without you being here in the debate - yet) placing his Air Malta plane as he has done, because we now have 'dead' tarmac at the bottom that serves no purpose compositionally, as the whole aircraft is not in frame - i.e. nothing 'makes up for' its presence in the shot. I simply want to pull the aircraft down in the frame to see it all. As I said above - my hunch is that Colin did this as he believed A.net require him to centre the fuselage.
Maybe that is the nub of my issue with all this - if I look at a photo and like what I see it 'works'; if I want to 'get inside the frame' and move the subject then something is not working for me. With aircraft with cropped fins and squeezed in the top of a crop I want to pull them down, just as I would want to pull Mick's PIA example above to the right to make it look okay. But I don't want to pull my Red Arrows formation to the left - it works as it is.
We are back in familiar territory with this thread - 'photography' site vs. 'database'. This debate is all about 'photography'.