"Before the AAC news broke, sources told the Action Network that officials at North Texas, Rice, UTSA and UTEP had contacted the Mountain West about joining the conference. North Texas and Rice had the most serious discussions, but ultimately, the Mountain West decided to remain at 12 schools, sources said."
Brett McMurphy article implies the MW decided to stay at 12 before these schools decided on AAC.
https://www.actionnetwork.com/ncaaf/aac-to-add-six-schools-conference-usa-college-football-realignment-charlotte-fau-north-texas-rice-uab-utsa