the size of the clip in his hand clearly dose not reach to the gun housing when fully inserted, a few inches short, equal to the 1st small vertical line you can see on the cartridge. If I draw line from there to the center line of the gun I get 6 more shells. Not to mention the word Clip's in the photo caption.
The caption also says
magazines of which there is clearly only 1. Your misinterpretation of the caption is obvious...2 gun(s), 2 magazine(s), 2 clip(s) of ammunition
per plane...at least for whatever model of Stuka that is in the pic.

Your perspective is a bit off but not by far...if you look at the length of the mag in comparison to the shells in the clip the guy is holding you can see that when all 6 rounds are inserted, if one round is chambered in the gun, there is room for one more round...so a max of 7 per gun (6 in the mag and 1 in the pipe)...at least for a Ju-87G-1 by all accounts.
If the 7 round clip of AP being loaded in this photo is any indication...then as stated above would be true for a G-1 at least...6 in the mag 1 in the pipe.

as he pushes the second clip into the cartradge to fully load the gun. 
Again, perspective...the breach of the weapon is the width of 1 round inside the gondola housing not 6 or 7...using the top photo, measure the length of the ammo clip and then measure the length of the extruded portion of the magazine...then look very closely at the front of that gondola housing where the barrel of the weapon sticks out...if you look at the diagram of the weapon without the gondola housing you will see where the breach housing is very large compared to the barrel...and in all of the photos none of the gondola housings are wide enough to hold a 6 round clip of ammo internally.