Self-assembled InGaAs/GaAs quantum dots (QDs) are of particular importance for the deterministic generation of spin-photon entanglement. One promising scheme relies on the Larmor precession of a spin in a transverse magnetic field, which is governed by the in-plane
g-factors of the electron and valence band heavy-hole. We probe the origin of heavy-hole
g-factor anisotropy with respect to the in-plane magnetic field direction and uncover how it impacts the entanglement generated between the spin and the photon polarization. First, using polarization-resolved photoluminescence measurements on a single QD, we determine that the impact of valence-band mixing dominates over effects due to a confinement-renormalized cubic Luttinger
q parameter. From this, we construct a comprehensive hole
g-tensor model. We then use this model to simulate the concurrence and fidelity of spin-photon entanglement generation with anisotropic hole
g-factors, which can be tuned via magnetic field angle and excitation polarization. The results demonstrate that post-growth control of the hole
g-factor can be used to improve spin-photon cluster state generation.