I'd ditch the tree or make it less dominant somewhere in the background. Probably do some cliffs/rocks instead, cause right now it looks like an archviz scene with two scifi elements just stuck in it. The red soldier also blend with silhouette of the tree, especially since colors (black and red) are similar on both character and tree.
I'd also work on inner logic a bit. If he's waiting to board the Thunderhawk, then there should be some space for that vehicle to land. It's probably not gonna land into the river. Not sure vertical aspect ratio is good for epic shots like this one. It may work out in some cases, but for this, I'd try regular 1.5 aspect ratio (not 1.778, to get more vertical space).
Lastly, you may wanna use box with volumeMTL instead of global volume material, if you are not doing so yet. It will render faster and be more controllable. And of course single bounce only volume, otherwise you will never render it clean ;)