Can someone explain to me how XM800T is 9.0 but Type 87 RCV is 9.3

Please someone explain me this logic, after recent BR changes, especially if there is someone from Gaijin on these forums. Because I would like to understand this.

Because XM-800T was battle rating 8.7 and Type 87 RCV was battle rating 9.0; that’s called decompression. Furthermore Type 87 RCV is much better than XM-800T thus it has a higher battle rating, but Type 89 is vastly superior, it still is at battle rating 9.0.