My thoughts,
If the viewer has to understand a lengthy leadup to understand your diorama, you've failed to get your point across. The picture or diorama is the story, or gives enough visual information to allow viewers to surmise their own action or ending and input their own understanding or viewpoint of the story. Sort of "a picture is worth a thousand words."
I would angle the corner of the house and offset it a bit so it visually bisects the base. This will give you a longer road for your sdkfz and a shorter ground for your partisans. By doing so it will reenforce the idea that the ghetto inhabitants were pushed back to their last stronghold and were fighting a desperate fight. A sort of last stand. Where as the Germans had all of Warsaw to maneuver around in. As for the proximity to the vehicle, it was house to house, alley to alley, sewer to sewer. Not alot of room and the layout will reflect that. The onlooker isn't sure who the winner of that battle will be but the placement will help create tension in the scene. When you're facing someone with a panzerfaust, you're always too close. Or maybe the partisans were surprised and didn't expect the motor infantry.
You can get away with unrealistic distances in a diorama because it would be unrealistic to use scale length. i.e. if you do a vignette of a sniper, you couldn't realisticly put sniper and target in the same scene. But you could put one side trying to draw the fire of a sniper (and never really show the sniper, you wouldn't have to because they're not sure where he is either, its why they are trying to draw his fire) or put the sniper in his position and know that somewhere out there , someone is going to have a bad day.
You wouldn't necessarily have to make a tall building or even a whole building. A ruin or wall or garden wall would work and ceate the same visual separation from the two groups. But if you really wanted to make the building, roof and all, you could add a figure or two on the roof getting ready to drop a grenade or moltov cocktail on the sdkfz, maybe the partisans on the ground are the bait for the trap.....
Mike
"Imagination is the dye that colors our lives"
Marcus Aurellius
A good friend will come and bail you out of jail...but, a true friend will be sitting next to you saying, "Damn...that was fun!"