you can do the maths yourself when you find the graph isn't clear enough
i guess this is the graph you are talking about.
From the game settings, you know the game is 0% sr, which means that there's no luck and decimals are always rounded to the nearest integer.
attacking with 1 army you kill 1*0.6 = 0.6 armies, which gets rounded to 1 (so you see in the graph with x=1 y=0.6)
i really don't understand which was your doubt