Electron correlation effects are often invoked as possible causes of differences between experimental and Hartree-Fock Compton profiles. The shape as well as the magnitude of these differences can be very different, depending on materials. In order to illustrate this, we performed post Hartree-Fock calculations on small LiH and MgO ionic clusters. The subsequent correlation corrections significantly improve Compton profiles and structure factors versus their experimentally determined counterparts. The opposite trends observed at small momenta for experimental deviations to Hartree-Fock Compton profiles of LiH and MgO are then qualitatively explained through an empirical model for a confined two-electron anion. This model further suggests that the confinement of the embedded anion favors the angular correlation mechanism.