At Lasham, our DOC was 25nm up to FL100 for the air/ground frequency. Mind you, sharing a similar frequency with Bristol Radar, I would often have chats with pilots having 'finger problems'. In theory I should have not transmitted in response, but being air/ground, I had no idea where Bristol was
During Lockdown 1, I had a lengthy conversation with a BBJ over mid S Ireland at FL410. The American crew had never heard of Lasham! Outrageous I thought! I even tried to convince them to get the Boeing maintained in Hampshire!
The TX power was limited to whatever wattage is prescribed by OFCOM, but being sat on top on a hill and with a decent Jotron RX/TX system installed, operational coverage was excellent.