I'm confused about the meaning of "total dimensions" when Qantas refers to their 2 piece baggage allowance.

Our flight with Qantas allows 2 pieces at 23kg each. Total dimensions of the 2 pieces must not exceed 270cm (106in) with no 1 piece exceeding 158cm (62in).

We have some plastic trunks that are 62in, but that only leaves 44in for a 2nd piece. That is really small for checked luggage, even smaller than the 45in carry-on baggage allowance. So it made me wonder if "total dimensions" possibly refers to the dimensions of the two pieces when stacked together. I kind of doubt it since I would only have to count one of the dimensions twice that way.