It turns out the sound and balances in the orchestra of War Memorial Opera House really are, uh, interesting. It seems a difference of all of eight feet has a noticable impact on the sound quality.
For complicated reasons I'm not going to go into, I saw the entire Norma performance last month from orchestra rear Z-104, while my companion saw the first act from ZZ-101 (the very back row, where the seats can be moved around to make space for patrons who use wheelchairs or scooters and their friends) and the second act from Z-102. He later reported that he'd thought the sound slightly better from Z-102 - a little muffled in row ZZ, and less so in Z. He's not a musician, but he is a good listener and musical, with a good enough ear that he easily picked out the best of the singers (Mishura) and knew there wasn't significant competition for that title. I definitely trust what he said about the sound quality.
I had my own minor revelation when I reviewed Fidelio. I was in around row M, but just off the right-hand aisle - not the one by the wall. It was not difficult to hear the singers' voices expanding into the house, an effect you miss in orchestra rear, where I feel more as thought the voices are aimed directly at me. But there is a disconcerting sensation of being out of the line of fire when you're hard left or right, plus there can be a distracting sensation that the voices are echoing off the wall.