Possible reasons that confinement resonances are not observed in a recent photoionization experiment on the endohedral fullerene Ce@C82+ are explored. The effect of the polarization of the fullerene shell in response to the ionization of the endohedrally encaged atom A@Cn, termed the shielding effect, has been investigated and found to be relatively small; no more than a 20% effect near threshold, and much less at higher energies. It is argued that most likely, the absence of confinement resonances in Ce@C82+ is due primarily to the finite thickness of the carbon cage; the off-the-center position and thermal vibration of the encaged atom, discussed elsewhere, further weaken the resonances rendering them beyond the sensitivity of the experiment to detect, in this case. For other situations/endohedrals, the confinement resonances should well be observable, and Ne@C60 is suggested as an excellent candidate.
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