Okay, I've seen guys do it two ways.
Way 1 has it so that the a7a straps go around both the 64 bag and the valise, so when tightened, they squish everything towards the centre of the frame.
Way 2 has it so the a7a straps only compress the valise (and whatever additional cargo you may have), but this leaves a lot of slack and a gap in between the valise and bag.
Is there a preferred method or whatever one finds practical/comfortable?