C4 axions in Type IIB Calabi-Yau compactifications of string theory have been extensively phenomenologically studied. Typically, the effective field theory is obtained from the tree level Kähler potential of Kähler moduli, where parametric control over the $\alpha'$ expansion is understood in regions of moduli space where all subvolumes are sufficiently large. Here, we include $\mathcal{N}=2$ corrections to the Kähler potential at tree level in $g_s$ but to all orders in $\alpha'$. This allows us to study regions of moduli space close to Kähler cone walls where the worldsheet instanton corrections converge, namely walls that correspond to flops between birationally equivalent Calabi-Yau geometries. This additional region can be of significant measure, and also potentially allows one to access phenomenologically interesting properties like larger axion decay constants.