Option 1 (Recommended)
Ensure that your cornered UX panels are solid-backed by running a bead of adhesive along the panel (foam or stud) 2" from the corner. Just before installing drywall, place a bead of adhesive on the foam near the corner. The drywall is bonded to the foam and the foam has been bonded to the concrete.
When installing drywall, float the corners by screwing drywall into nearest attachment studs. This is a common practice for professional drywall installers because the InSoFast panels provide solid backing for the drywall.
Place a bead of adhesive approximately 1" from each side of the corner. Press 2" x 2" - 25 ga. sheet metal angle into adhesive. Attach drywall by screwing into the metal corner angle. Nail into intersecting stud. Attach drywall by screwing into the metal corner angle.