I’ve been playing with maps. Here I set the proposed building on a contemporary OS map to see how naturally it sits – the answer? Not badly; the pavilions are among the cluster of observatory buildings in the right hand corner.
This, meanwhile, is an 1873 OS of the observatory site. It shows more of the landscape, and more of the cluster of buildings, a fair few of which no longer exist, pulled down to make room for new and different experiments. The proposed scheme sits to the east of Blackheath Avenue, and here you can see the difference between the alignment of the landscape elements, parallel to the avenue, and those of the pavilions which follow the north-south meridian line.