ImperialFighter said:

As far as the 'circular rims' of the turbines go, they *aren't* a perfect circle as you say...although I've seen some X-Wing images where they are wrongly shown to be. (I actually amended my last line in the post you quoted, to clarify that various 'google' images of them seem to vary)

But here's an image which gives a decent look at how the top and bottom halves of the 'circular rims' are intended to be slightly mismatched with each other - http://img3.wikia.nocookie.net/__cb20150309054138/starwars/images/b/b2/X-wing_2_Fathead.png

Are you sure that that's not just a trick of perspective combined with the shelf jutting out a little?