Point in time restore from RMAN backups taken from physical standby database

Oracle 11.2.0.4

I'm taking full and incremental backups of the standby databases.  While testing a point in time recovery to a time in the past I'm having trouble opening the database.  (I'm testing a recovery scenario where I'm restoring to a point in time in the past to recover from a logical corruption).

On the standby databases I'm taking full (inc 0) backups on Friday and incremental backups (inc 1) on Sun - Thu.  

These are my backup steps.

    crosscheck backup;

    crosscheck archivelog all;

    backup archivelog all not backed up 1 times tag='20190119_arch';

    delete force noprompt obsolete;

    delete force noprompt archivelog all completed before 'sysdate-${ARCHIVE_RETENTION}';