It's a trick of the eye, because its a small 3rd tier. In reality, the back of the Top Balcony towards the Park End is only similar in height to the roof of Park End and, by association, the Bullens and Gwladys, which are all dwarfed by the new stands. My seat in TB, and im Row G, so about half way up, is roughly at the level of the Park End roof, which unfortunately means i can see the Hole Punch. Towards the Glawdys, there are probably about twice as many rows, so at the very back, it would probably be about 15-20 metres higher(?).
To give you an idea, the current park end stand, with a much shallower viewing angle, holds about 5,700. The new single tier South end stand will hold more than double at around 13,000.