If you're in the front row of the balcony, leaning forward will make you the devil. There is a special circle of hell for people who go "I cannot see 100% of the stage, so I shall lean forward". Brilliant! Well done! Now the people behind you can't even see 10% of the stage!
... sorry, I've had some issues with the balcony of the Novello recently. XD Take out the hyperbole and ire, and it reads "ooh, I wouldn't advise leaning forward, it might block the people behind you, and that would be very upsetting for them

".
I don't know much about the ROH myself, so this entire paragraph is going to be semi-educated guesswork, I'm afraid.

I was looking at ticket prices online the other day, not sure whether to be more aghast at the prices themselves, or at the fact whole performances sell out even with such prices, and £80 sounds fairly low, for ROH prices. I don't imagine it'll be any worse than front row balcony of any other theatre; you'll be in the top section (boo!) but there won't be anyone in front of you (hurray!) but there probably will be a safety bar in your line of vision (boo!). And there's no way in hell it can be anywhere near as bad as comparable seats at the Coliseum. Anyone who's sat in the cheap seats for ENO say aye!
The message itself sounds like what you might be losing is the very front lip of the stage. Really, I've had worse seats. Admittedly for a mere 16th of the price. XD But the ROH is absolutely not a cheap night out, and the £80 that would guarantee you the most luxurious and well-placed seat in the whole place with ushers massaging your feet in any other theatre sadly won't see you so far at the Richly Overpriced uh... House.
If in real undoubted terror, phone the box office. They're pros, they should know?