In the case of the tape job, it is not possible to disable the Full.
Even when using forward forever incremental on the disk backup, the tape job always needs a Full (normal or Synthetic Full) to build the chain and write everything to tape. For this reason, the Full schedule in the tape job cannot be removed.
“You can customize the virtual full backup schedule according to your needs, although you cannot disable the virtual full backup if you back up the forever forward incremental backup chain. Also, you cannot create more than one virtual full backup a day.”