SM 9.34 Incident - keep default impac and emergency when I choose a CI

Dear Expert,

We define CI in SM. On CI records, we do not define Priority and Default Impact fields.

When we create a incident Impact and Emergency fields are filled by default, but when we choose a CI, these default informations are erased : blanked field because we do not define them in CI records.

Is there a setting witch does not reflect the Ci's impact and priority and kepp the default of incident.