Pretty ambitious project, Connor.
I agree with Jerry that you should maybe give your composition some more thought.
You should have a single main point of focus which tells the story you want, with the rest of the elements arranged around that to support that idea and help bring the viewer's attention to it.
I see two ways to do this with the elements you have selected:
As Jerry suggests, you could make the scene smaller which has some very good advantages, not the least of which is an intense focus on the main idea.
Alternatively, you could go for a larger composition, but that will require some planning and testing of the arrangements of the elements being used.
All of the elements should be arranged to balance the scene with your main focus more or less at the center of attention. Don't forget that the terrain and elevations can be used to make the arrangement logical and at the same time visually balanced. Also, think in terms of not just left to right and higher or lower, but also of front to rear.
Here's how I might work out the composition to the initial mockup phase:
To me, the most dramatic (and therefore strongest and most interesting) part that you've shown are the troops engaged in the hand-to-hand combat. However, if you have all of the other German troops coming into the scene from the same side as if they're coming to help, logic suggests that the space needed for them will push the main focus (the hand-to-hand combat) over to one side.
I might suggest that you position the group of troops firing their weapons in fighting positions off to the right side of your diorama, the hand-to-hand combat in the center, and the troops rushing up to reinforce the Soviet penetration coming into the scene from the left side front.
So, perhaps imagine a German fighting position (a trench line or series of hasty positions) running from the right front corner of your dio to the center rear.
In the right front corner, you have the Germans in postion firing and engaging targets that are off to the right front, but off the actual dio.
In the center rear, perhaps slightly elevated, you have the position being overrun by the Soviets and the desperate hand-to-hand combat.
Coming into the scene from the left front towards the center rear, you have the German reserves rushing to seal the breach.
If you elevated the right front to the center rear, you could have the left front at a lower elevation so that the reserves can approach from cover.
Perhaps the scene then becomes a hilltop position rising in elevation from the right front to the center rear with a road cut and embankment paralleling from the left center to the front center. This could elevate the center of attention at the rear with the hand-to-hand and the supporting "cast" in slightly lower positions in the left and right front corners, with the right corner being somewhat higher than the left.
Here's a quick sketch of what I'm trying to describe:
Looking at this sketch, I can see that the center foreground might need some more work - maybe curve the position on the right down some more or perhaps just some interesting detail with the terrain (but nothing so visually strong that it detracts from the main elements). The whole composition might be condensed into a smaller footprint?
This still makes for a very large dio, but something like this might help to balance the elements and put the main focus nearer the balance point while still allowing you to use the figures posed more or less as they come from the box.
Note the "golden triangle" which creates symmetrical balance from side to side and front to rear, and also concentric balance focused towards the center of the scene. If each of the main elements are at different elevations, this same kind of balance is retained up and down height wise.
(The "rule of threes" or the "golden or magic triangle" can be very helpful, but sometimes a little too formulaic. Still, it does work which is why artists have been using it for centuries to compose their works.)
You can test (mockup) your composition out by positioning your figures (even while still WIPs) and using books or something to provide changes in elevation. You can use rulers or even pieces of string to mark out lines and edges. If you do this on a table, you can walk around and look at your composition experiment to see what the best viewing lines are. Play around with things until you have the scene the way you want, then use the edges of paper sheets or rulers to lay out your diorama's edges so that the best view is from the direction you want and you've eliminated as much "dead space" as you can. Now sketch it all out either in 1:1 or smaller with the dimensions recorded.
Like I said, an ambitious project, but possible with some planning.
