WOW! First off SaintToad, Thank you very very much for a very helpful and informative critique. You basically nailed every problem and issue I'm having with this piece right on the head, especially the part about disguising order!
I will definitely take a picture with all the elements on there.
In consideration of some of your suggestions, I am going to try and fix the fuel tank and the barricade. I may cut my fuel tank and only put in the front section. Hopefully that will help with my line issue. Not sure if I can move the barricade around, but there is going to be a lot of scattered junk around it. I'm also going to redo the concrete area..that's supposed to look like a destroyed imperial runway/landing pad.
As for height variation, the front will have the rockets in the air and the back will be framed more by my tower (it's going to be taller when it's complete). My initial plan for this piece was to make it look like the orks were launching the grot bombs from a "safe" distance, so that's why a lot of the details are at the back of the diorama... of course that doesn't really help with my flatness issue lol..
I think the height of the tower will be the only thing that really frames the entire piece in the end; it's supposed to look like it was built at the beginning of a tall mountain. The illusion I am trying to achieve is that this imperial landing pad is nestled in the mountains, and has since been taken over by orks and converted into a launch pad.
Once I figure out the fuel tank and the size of this piece, I will be adding A LOT of scattered junk... pipes, fuel tanks, wheels, gas cans, random ork parts, etc. I think I'll add some imperial bits too, to show that there was some imperial presence some time ago.. actually, now that I think of it, some of the bits I used for the barricades belong to Space Marine tanks, so hopefully that'll help with the narrative.
Again, I thank you very much for your help and your most excellent suggestions. I will be applying what you've taught me to this project, as well as my future projects. THANKS THANKS THANKS!!!