I have checked a little more about the major Cumberland diamond.
For Queen Victoria's Regal Circlet I had always thought the Cumberland had its own setting, as an alternate element, to sit above the band, and not on the band.
My view seems supported by Crown Jewels 1998.
It states for Queen Elizabeth's Crown that the diamond of the Sultan of Turkey that is in the central position on the front of the band of that crown was in the same position on Queen Victoria's Regal Circlet, which was stripped of its diamonds to make Queen Elizabeth's Crown.
--Previous Message-- : : : Thought I'd post the Garrard ledger page for : Queen Victoria's Regal Circlet and my : transcription of it.