The points I'm trying to make are:
- Sheer volume of VMC glider traffic calling a LARS is likely to overwhelm the unit with calls from gliders who, whilst they'll know where they are currently, don't have any idea where they'll be ten minutes later - there's times where I'll be at 5000' one minute and then ten minutes later I'll be at 500'. During that time I may have covered 20NM in any direction (including backtracking). A call to a LARS (if we can all decide which one to use) would result in something like "Glider 123 is operating in Open FIR in a height band between ground level and controlled airspace in the Oxfordshire area" is sometimes as accurate a report as I can get. This isn't going to help the controller and it's not going to help any power pilots either.
- In IMC conditions there may may again be a high volume of gliders unable to comply with RAS requiremenets (see doc
http://www.caa.co.uk/docs/33/ga_srg_07webSSL08.pdf - "You must also inform the controller before making any other changes in heading or level" - in a glider that would require constant radio calls!).
- In IMC, while in cloud, there'll be a much lower volume of gliders in cloud (and they'll have a better idea of where they are whilst climbing but not whilst cruising)
FYI, ridge soaring only works in certain wind conditions and assumes that the pilot is attempting to ridge soar - so there's no guarantee which route a glider pilot will take. The locals will probably stick to a preferred route which is known to produce suitable conditions - the Southdowns being a good example. Non-locals won't known any better!