Talking about recieving different broadcast regions, after switch over my Gran could still get the PSB MUX's from Wales (Wenvoe) as well as the correct region, West/HTV, from Mendip, this being in a house high up in Crewkerne, this was even despite them being in different directions (though Wenvoe is the main station for BBC national FM). She would also have been in the usable signal area for Stockland Hill (Westcountry) and just about able to receive Rowridge (South) from the IoW, Radio Solent from Rowridge can just about be picked up.
Where I live on Portland it's a mix of Rowridge and Stockland Hill as whilst Stockland Hill is closer it's at a much lower power and some people just prefer news from the south.
Interestingly the correct region is in theory Westcountry as that's what the Weymouth relays use (well the Weymouth relay does use Rowridge for BBC National FM) yet a Sky or freesat reciever will default to the Southern region for some reason.
Another transmitting oddity that no longer exists is Welsh opt-outs on Radio 1, the Chard FM relay has an extra receive antenna on North Hessary Tor for Radio 1 due to this whereas everything else uses Wenvoe as the re-broadcast feed.