A note on the magnitude of the flux superpotential

The magnitude of the flux superpotential W _flux plays a crucial role in determining the scales of IIB string compactifications after moduli stabilisation. It has been argued that values of W _flux ≠1 are preferred, and even required for physical and consistency reasons. This note revisits these arguments. We establish that the couplings of heavy Kaluza-Klein modes to light states scale with the internal volume as g ∼ M _KK /M _P ∼ ^-2/3 ≠1 and argue that consistency of the superspace derivative expansion requires gF/M ² ∼ m _3/2 /M _KK ≠1, where F is the auxiliary field of the light fields and M the ultraviolet cutoff. This gives only a mild constraint on the flux superpotential, W _flux ≠^1/3, which can be easily satisfied for (1) values of W _flux. This regime is also statistically favoured and makes the Bousso-Polchinski mechanism for the vacuum energy hierarchically more efficient.