Low gear/high gear threshold for RBG

[Decentsmartserb]

Hello there, I am curious if anyone know what's exactly the limit between lower gear tier RBG and higher gear tier RBG?
Is it specific rule or overall gear score that you shouldn't go over to remain in lower tier? Like 5k is limit or something like that?
Any information is appreciated

P.S. Nevermind, we found out.... 5.7k without purchasing any ICC heroic allows you to be maximum geared and still actually play RANDOM battleground vs random players , not premades on both sides.