I think you've just hit the nail on the head. If the touch judge has an opstructed view of the defensive line at the PTB, they're offside!

Touch judge's officiating offside makes sense to me. Leaves the ref to watch the PTB.

Is it correct though?

Just because the Australians do it first does not mean we are just copying. Perhaps it is the right thing to do and we should have done it ourselves first.

Look at RU copying League on lots of things these last few years, have those choices been wrong?

Who's offside? The player getting back into position who isn't interfering with play? The player in the middle of the field, 30 metres from the touchjudge? Let them onto the field, and they'll see a lot better.

With the communication systems between referee and touch judge they have in place, the TJs are effectively policing offside anyway- listen closely to the ref's microphone on televised games and you'll hear them telling players that the TJ keeps picking them out for offside so to make more of an effort getting back.

Personally I'm in favour of only having one person making decisions out on the field however. Getting more people involved in the decision making process can add to inconsistency and confusion rather than provide clarity - see the final play of the playoff game away to Wigan last season as a perfect example of TJ, referee and video ref working in anything but perfect harmony.

I agree with Gotcha and Richie. This is worrying.