@sroychow in the premixing case this input needs to be customized.  See please how it is done here:    https://github.com/cms-sw/cmssw/blob/9e912a119e2bf295939ef033dbc5fb485df778c9/Validation/SiTrackerPhase2V/python/Phase2TrackerValidateDigi_cfi.py#L129-L135