I'm sure this has been covered and may even be in the user manual, but I haven't been able to locate this information.
Regarding the forever full incremental, how are deleted files handled? When the number of incrementals exceeds the number of retention points and the earliest incremental is injected into the full backup, if files were deleted between the time the original full backup was taken and the first incremental, will those files be deleted from the full backup at the beginning of the chain? In this scenario, it is conceivable that the size of the original full backup will fluctuate up and down. Is that the case or if data is injected into the full backup is it retained 'forever'?