Relative location of helium ignition within the accreted helium envelope (M_He) in relation to the mass of the helium envelope. The relative location is given by the dimensionless variable χ = (m(T_max)−M_WD,i)/M_He. The green points indicate that the WD experiences helium deflagration; blue points indicate helium detonation. The hollow circles indicate BABDef systems. Groups resulting from different initial WD masses (M_WD,i) are indicated. The dashed line indicates χ = 0.