I completely agree, they will easily be able to obscure anything they need to.
The Shard in London is 306 m (1,004 ft), Because of the buidlings etc, you only capture glimpses down the streets every now and then and can't see it till the river. (Distance from the office as the crow flies 0.5 miles)
One Canada Sq in Canar Wharf London is 235 metres (771 ft), and again, you can never see it till the river. (Distance from the office as the crow flies 2.5 miles)
Even the London Eye at 135 metres(443 ft) is difficult to see until you get to the banks of the Thames. (Distance from the office as the crow flies 1.8 miles)
I can't see any of the buildings from my work