Hi
Setting the bomb delay sets the AB canister release delay, depending on altitude and speed this effects the dispersal.
Try using the Stuvi bombsite, on the Ju88A4 I used to find diving at 480mph Stuvi set to 1200m and 5 second delay work ok on the AB500's
With Stukas I found the results to unreliable to take the payload on a mission, and forget level bombing with the 5 ringed AB1000.
Any Russian American similar armament works ok, probably too good
As already mentioned by Gunkan
AB bombs are too ineffective to use, you might as well take normal bomb load outs.
Add to that
German 2x SC 1000kg
Almost half as powerful as
Japanese 1x 800kg
German bombing loads have been seemingly nerfed over the years
Bug reports fell on deaf ears at 1c years ago after I reported the SC2000 bug, they fixed it, then the next patch come out and it was nerfed again and still is.
Edit> just dug up some old IL2 notes on SC2000, its been designated a demolition bomb in city areas.