Playing around with the Ju-88A4 I was looking at the different gunner positions and when I get to the radio operators position and see his two guns, one for firing aft left and the other for aft right, the thought occurs to me why didn't the Germans mount one gun with enough traverse to cover that entire upper rear arc instead of two separate left/right segments? Could have even combined the two MG's into one mount covering the entire upper rear arc, doubling the effective firepower.

I just find it odd.

Yeah, that is weird. Well, the whole darn plane is weird, and UGLY.

Not enough room to swing gun that far in the opposite direction inside, and still be able to aim it? Looking at diagrams, it seems the butt of the MGs were pretty much in the gunner's face. Since it was not on a ring or turret, to aim it 45 degrees right, the rear of the weapon would probably have been so close to the left side of the canopy he would not have been able aim down or probably even operate it at all. When American bombers depended on a single 1 or 2 MG mount for a similar firing arc, it was either in a turret (such as B-25 or TBF) or a ring mount (TBD or SBD/A-24) where the weapon rotated on a axis around the gunner, or a window mount where the gunners whole body could pivot opposite the MG barrel and site (B-17 waist gunner).

Originally it had a single gun. The Il2 model is a later aircraft with two armoured guns. Wider firing arc and possibly less in the face of the radio operator as suggested above.
The fighter variants with the solid nose looked much better. More like the prototype, especially later on when the gondola was removed.

I'm looking forward to the Ju88C6 which is one of the first fighter variants. Still carried the two armoured rear guns but the glazed nose is replaced with 3 machine guns and a single 20mm cannon. It's not as exciting as the later variants with radar, gunpods and schrage muzik but it's getting closer.

Of course it is a weird design, it was made by US constructors
A whole two-gun turret would have added more weight even without electrics to power it, also space was restricted. The Ju 85-88 medium bombers were initially designed in the mid-30ies to be fast attack planes (fast enough to let fighters behind them, or hunt other night fighters like Mosquitoes in the later war with the 88-388 versions), the second gun was installed later as a second thought when some allied fighters became faster than the Ju; the rear glass and surrounding cladding was also bulletproof against shots frome the rear.
From all i read it was a delight to fly, fast, turned on a dime, and generally very well thought out. Not much medium bombers going at up to 625 km/h while carrying 1000 kilograms of bombs, torpedoes or all kinds of weaponry, while being able to bomb horizontally, or at a dive, or hunt other fighters.
Fw Stahl writes that the types from A4 on were able to let most enemy fighters behind them in a climb, with the engines at full 'Kampfleistung'.

Which poses another question, since i just bought BoS, can you add/buy the JU 88 for that version, or do you have to buy Battle of Moscow to get a flyable JU 88 ?

Asked in the IL2 forum, you need to buy the 'Battle of Moscow' to virtually 'fly' a JU88, you cannot get it as a single buy.
I just bought BoM, price is at 20 Euros/Dollars right now, makes 2 per plane. No I am not related to the franchise ..
All the best,
Catfish

Unbelievable what you find on the 'net, from your armchair ...

Nice video... an interesting comment from a Ju 88 pilot in that video... ''we got rid of the cannon as it took up too much space, and it also got rid of the weight so we could fly faster''... they also got rid of the dive brakes for the same reason. '' We didn't ask permission, we just removed them to give us more speed''