Love the picture Codlasher. I have never found BLEs in such numbers. As you will be aware, bats move roosts regularly and usually have several in an area. I know of four CPip roosts within my village and I am sure that they will all be part of a larger community. However, without radio tracking I won't be able to prove it.
I understand your point on the use of roof voids and buildings as roosts but several bat species have only been found in tree roosts. Therefore, it is essential that as many trees with potential roost features are surveyed correctly prior to any work being conducted. This is why the key produced by Henry is, in my opinion, going to have a great impact.
I am always available for advice should you need it, but here's one you haven't asked for: if you are considering an upgrade to your bat detector then the Batbox Duet is an excellent alrounder. Coupled with a decent MP3 player you can get great recordings that can be analysed with freely available software when call diagnosis is difficult in the field.