Infrastructure

In England, 60 miles (100 Km) from London, using a local cable connection;
On your standard download page, http://www.libreoffice.org/download/libreoffice-fresh/, I requested LibreOffice 5.2.1 for Win x86
The request was met (after a significant delay) from the server/file http://mirror.vutbr.cz/tdf/libreoffice/stable/5.2.1/win/x86/LibreOffice_5.2.1_Win_x86.msi
The download crept like a snail, so I abandoned and opted to choose a mirror manually.

I found that, according to the list of mirrors on page I was shown, the 'preferred mirror' for my location was mirror.vutbr.cz. I also saw on that page "Found 1 mirror very close.. ..http://mirror.vutbr.cz/tdf/libreoffice/stable/5.2.1/win/x86/LibreOffice_5.2.1_Win_x86.msi" - yes, really close eh?
I looked on your map of mirrors and was shown that it indicated that mirror as '1' for me, despite the existence of servers in London (100Km away), France, Netherlands etc etc.

On the manual mirror selection page, under "Found 3 mirrors which handle this country (GB)", I opted for http://mirror.catn.com/pub/tdf/libreoffice/stable/5.2.1/win/x86/LibreOffice_5.2.1_Win_x86.msi
which downloaded at a steady 1.9MB/s. (B, not b)

However, I then tried to download the en-GB Help-pack (LibreOffice_5.2.1_Win_x86_helppack_en-GB.msi) by going back and clicking the appropriate button on the 'normal' download page. I was yet again directed to mirror.vutbr.cz.

I did not see any option to circumvent this on the'manual mirror selection page, so I went to the directory (luckily accessible) whence LibO itself had downloaded (mirror.catn.com/pub/tdf/libreoffice/stable/5.2.1/win/x86) and tried the en-GB help file link there. Since it was a '.msi.asc' file, that was no help. However, I discovered that taking its address, removing the '.asc' from the end, and submitting the resulting address to the browser, I was able to download the en-GB Help pack.

Then, since I have two Win systems, I had to go through the whole rigmarole for x64 versions. Same story but at least, when mirror.vutbr.cz was again thrust at me, I was prepared for it and knew how to get both files from the correct local and much faster site.

I suppose that many UK users would not have realised what was happening to them and would have sat fretting while their files came, extremely slowly, from entirely the wrong mirror.

In summary: Using default download route, UK user was served LibO 5.2.1 from unusually slow Czech mirror instead of local UK mirror which was very much faster.