Got most of my decos in 1-4.
Used 1CV with 3 of my best torp bombers and 1 fighter (used Graf Zeppelin, cause i want to lvl her), 4DDs (one Akizuki class with AACI) and one 4 slot CL/CT.
First i used 4 skilled lookouts and 1 searchlight and got about 1 drop in 3 sorties, after switching to 4 skilled lookouts and 3 searchlights i got a deco drop almost every run.
But i didn't spam the map, just two or three runs every hour and some daily quests and WoWs matches in between.