Why not? There are quite a few trains which have RSA's like this.For example, 17209 (CCT-SBC) is an SCR rake, and has an RSA with 17235 which runs between SR and SWR (SBC-NCJ). Some other pairs that have such an arrangement are 12163 and 11063 ( CR train, RSA at SR end), 16021 and 16023 ( SR train with RSA at SWR end).