Hi,
It's all to do with which level is free in the CPT area.
FL190: BB/BE/NX deps
FL180: LOREL1S arrivals
FL170: GD/VN/DL deps
FL160: SS CPT deps
FL140: OCK arrivals via G1
FL130: LL CPT deps
FL110: HH/HI/LF inbounds from North
FL100: HH/HI/LF deps to North
So its really a case of find a gap and fit into it.........Not ideal, we know..........but safe !
Cheers