Hmm I think that straight line distance measurement is just the geographical distance from your premises to the exchange, not the actual cable length.
If you take the cable length into consideration it's usually longer, sometimes quite considerably longer too.
Using that checker it claims that I am 5.26km away from my exchange, however I know for certain the length of my line exceeds 6.5km.
It sounds like your line has similar characteristics as mine, so either you have aluminium in part of your line or your line length is considerably longer than 6.5km or possibly corroded wire is causing you to have a noisy line which is filtering out the DSL signal.
If you take the cable length into consideration it's usually longer, sometimes quite considerably longer too.
Using that checker it claims that I am 5.26km away from my exchange, however I know for certain the length of my line exceeds 6.5km.
It sounds like your line has similar characteristics as mine, so either you have aluminium in part of your line or your line length is considerably longer than 6.5km or possibly corroded wire is causing you to have a noisy line which is filtering out the DSL signal.