I find the geo "accuracy" of the various PPPoE ISPs can vary quite a bit. A lot of IP geolocation sources will actually be getting their data from companies such as Maxmind - you can try your own IP on their site: https://www.maxmind.com/en/geoip2-precision-demo
My home IP on BT FTTC is dynamic and can be from quite a wide variety of BTs IP ranges, yet Maxmind always puts me in a town about 10 miles away. My mobile on EE odly can also give some 'localish' locations at times and at other times vary.
Some previous ISPs would always stick me in Warrington, Newbury, Sheffield etc (Spot the ISPs!!)
I would love an insight into some of the additional data sources that Maxmind obtain to enhance their geo, funnily enough they keep that close to their chests.
But safe to say from IP it's never that accurate to know exactly where you are, just good enough to serve you those lovely "Want to meet mythical unicorns in Blah Town" adverts and try an make some money out of you!