It is clear from the 3D structure that the axial hydroxyl group is hindered more by the Me group as compared to the equatorial hydroxyl group.

When a compound is oxidised, the equatorial group is oxidised faster compared to the axial one as the axial attack is very sensitive to steric hidrance with rate constants reduced significantly as a result of increased substitution.

Equatorial attack is also impeded but to a lower extent. This stereoselectivity is mainly enthalpy controlled with axial attack requiring more activation energy than the equatorial attack.