Here’s some photos, taken on 3 May 2016, to illustrate what the Berry and Balu parties would have been able to see from the balcony of apartment 606, on the evening that Madeleine disappeared.
First of all, this is facing the Tapas reception, to make it clear where the photos were taken from. I took the first where the curved step in the top of the wall is on the, the second where the rectangular step in the top of the wall is, and the third from the dead centre of the Tapas entrance.
First of all, here is the nearest view I could dig out of Google StreetView, dated Aug 2009, to get a better idea of the size of the trees back then.
Here is the view from a few metres south of the Tapas entrance. The balcony of 606 is the middle level at the far end of the block. The street light nearer to the balcony is going to become an obstacle, as you would have to see through a bright light to a dimmer locale at the Tapas entrance.
I have now moved north a couple of steps to where the rectangular step in the wall is. At least part of the balcony would be able to see this location.
Finally, this is from the centre of the Tapas entrance. Now the 2 trees are blocking any view of the balcony of apartment 606. This was taken at eye level whereas StreetView is from a camera mounted a few feet above the roof of a car. The vegetation to the left of the trees would prevent any decent view further north.
The Berry and Balu party was not acting as a neighbourhood watch. They were socialising, eating and drinking. The photos make clear their view is obstructed until someone enters the car park behind Block 6 or goes some metres to the south of the Tapas reception.
Perhaps they saw other people that evening, before Madeleine disappeared e.g. Jes Wilkins on his walk, but they didn’t see any of the key actions involving the Tapas 9.