DTTB Power Levels
Allowing for a variation of +/- 2 dB in the DTTB to PAL ratio (ɰ Km from the two tower transmissions in Sydney), and combining with the previous -8 dB restriction, a -10 dB DTTB to PAL ratio can be allowed without interference into PAL.
This is cautious worse case analysis with the information currently available.
Note that the sound of the lower channel is the restricting criteria. If the vision was the limiting factor a -5 dB DTTB to PAL ratio could be allowed.