Offloading Backup RMAN Burden to Physical Standby

My Configuration

a)  Backup Controlfile only on Primary

b)  Backup datafiles etc on Standby

c)  Restoration on new server

     1.  Take controlfile backup from primary

     2.  restore that

     3.  scp backup files to new server

     4.  catalog location of new files after restoring controlfile from primary

     5.  restore database.

d)  Does it make a difference when using the controlfile from the primary whether is should come before or after the backup of the secondary?  Should the two be coordinated - one immediately following the other?  I am trying to figure out why restores using the above process are working and sometimes not.