Yeah, the bouquets are (I believe) pulled from the broadcast stream - it's basically what your TV uses when you say 'here's my postcode/region' on initial setup, specifically to address what you're seeing: getting your local BBC One on 101 instead of somewhere else.
Again, I don't use them, but if you have a play then you should find your regional bouquet in there and can maybe work out how to use it to map channels to the Freesat EPG channel numbers. That would put BBC South on 101 for you, and perhaps even keep it there... downside is that BBC One HD is still national, so that ends up on 107 or similar, even though BBC Two HD is 102.
You may need to delete existing channels, though (not services), as the bouquets are an alternative to auto mapping.
And after that, we need someone who uses the things, so unless Mr Clarkstone wanders past (I'll ping him on IRC) or similar, my journey ends here, I'm afraid...!