The magic item Dimensional Loop (Acquisitions Incorporated, pg. 220) has an ability called Fold Space which says:
Choose a space you can see within 60 feet of you (no action required). You treat that space as if it were within 5 feet of you until the end of your turn. This allows you to move immediately to that space without provoking opportunity attacks, or to interact with objects or creatures in that space as though they were next to you (including allowing you to make melee attacks into that space).
Suppose Jim Darkmagic is having a dual with another mage, and they are 50 feet apart. The mage uses its action to hold a fireball spell until he sees Jim casting a spell. On Jim's turn, he uses the Fold Space ability of his Dimensional Loop and chooses the space the mage is occupying. Until the end of Jim's turn, the mage's space is treated as if it were within 5 feet of Jim. Next Jim starts casting inflict wounds on the mage. Seeing this, the mage uses his reaction to cast fireball centered directly on Jim.
Is the mage considered to be within the area of effect of his own fireball?
Similarly, does Jim need to be wary of casting his own fireball on the mage until next turn?