After a few weeks playing around with the APRS TNC in the car, I've noticed how much worse the range is than for FM voice. There is also a big difference in range between when moving and stopped, because of quick fading which wouldn't matter with voice.
I drove to Ingleton from Barrow, receiving my own transmissions at home on 144.800 MHz. No packets were received from me once I got past Lindal, until I stopped at the car park in Ingleton. There would have been areas I passed through on the way where the signal would have been stronger than Ingleton.
Some pages about packet audio and noise
The pictures below are the mast at Holt Lane near Preston. The 2 folded dipoles are for Lancashire County Council's trunked system in the 177 MHz band (data on 177.375 MHz). There are also 2 4-stack dipoles for Airwave. The folded dipoles are facing towards Blackburn, so there will be a null towards Billinge Hill where there is another council base station. The mast looks like it was originally for Cellnet (O2) analogue phones.
Another mast near Preston is at Windy Harbour. This is a higher site than Holt Lane, with a lot more antennas including what look like United Utilities 139 MHz dipoles with reflectors.