  Extracting reliable low-energy information from string compactifications
notoriously requires a detailed understanding of the UV sensitivity of the
corresponding effective field theories. Despite past efforts in computing
perturbative string corrections to the tree-level action, neither a systematic
approach nor a unified framework has emerged yet. We make progress in this
direction, focusing on the moduli dependence of perturbative corrections to the
4D scalar potential of type IIB Calabi-Yau orientifold compactifications. We
proceed by employing two strategies. First, we use two rescaling symmetries of
type IIB string theory to infer the dependence of any perturbative correction
on both the dilaton and the Calabi-Yau volume. Second, we use F/M-theory
duality to conclude that KK reductions on elliptically-fibred Calabi-Yau
fourfolds of the M-theory action at any order in the derivative expansion can
only generate $(\alpha')^{\rm even}$ corrections to the 4D scalar potential,
which, moreover, all vanish for trivial fibrations. We finally give evidence
that $(\alpha')^{\rm odd}$ effects arise from integrating out KK and winding
modes on the elliptic fibration and argue that the leading no-scale breaking
effects at string tree-level arise from $(\alpha')^3$ effects, modulo potential
logarithmic corrections.
