How does spellcasting interact with Improved Duplicity?


Trikery Clerics get this Channel Divinity option : Invoke Duplicity.

Starting at 2nd level, you can use your Channel Divinity to create an illusory duplicate of yourself. As an action, you create a perfect illusion of yourself that lasts for 1 minute, or until you lose your concentration (as if you were concentrating on a spell). The illusion appears in an unoccupied space that you can see within 30 feet of you. As a bonus action on your turn, you can move the illusion up to 30 feet to a space you can see, but it must remain within 120 feet of you. For the duration, you can cast spells as though you were in the illusion’s space, but you must use your own senses. Additionally, when both you and your illusion are within 5 feet of a creature that can see the illusion, you have advantage on attack rolls against that creature, given how distracting the illusion is to the target.

Which upgrades when they reach a high level : Improved Duplicity.

At 17th level, you can create up to four duplicates of yourself, instead of one, when you use Invoke Duplicity. As a bonus action on your turn, you can move any number of them up to 30 feet, to a maximum range of 120 feet.

How does spellcasting interact with Improved Duplicity ? In other words, could the spell originate from multiple (perhaps all four) duplicities at the same time, or only one ? I suppose only one, but it’s best to check.