Your personal hearing profile may look different from your audiogram. The Sound Check is testing for the way that you hear on the mobile phone. For example, if you use a hearing aid, your hearing is already being adapted by the hearing aid and so the profile will look different to a hearing test taken with the hearing aid out.
Also, different phones use different microphones and speakers. So, an unexpected hearing profile result could be as a result of your mobile. For example, a phone such as a Doro already has extra loud and clear sound which can help to improve your hearing.