My son is an out of state MS I at a big state U. He was able to transfer his 4 yr scholarship from GA Tech (out of state), which was more expensive.
At the time (we knew absolutely nothing and weren't thinking of the cost difference), we got the impression that an important factor in the decision was with the battalion he hoped to transfer into. We also got the impression that the admission folks really wanted him and advocated on his behalf with the battalion. They were able to offer in-state tuition to my out of state son, which may have helped.
Bottomline, your son should get to work NOW, making contact with his desired battalion and that school's admissions office.
As I said, at the time we knew nothing. It took my son about two minutes to realize that a number of folks did him a favor (being the only out of state 4 yr scholarship MS I in his battalion). It is a motivating factor for him, particularly as he surrounded by many well qualified and deserving non-scholarship cadets.
Best of luck