The way I'm connected appears to be underground ducts feeding roadside poles which them distribute to groups of 4-5 houses every 100m or so. My overhead cable is connected to a small metal pole on the gable of my house which appears to provide tension and then goes into a grey BT junction box. The output from this is two cable, one pair that no longer goes anywhere (so I've clipped and tidied) the other par going to the master socket inside the house (approx 5m run).
I'm wondering if the joint is an obvious point of attenuation and if it is worth getting Openreach in to replace the cable with a single run direct to the master socket? Maybe even getting it run underground whilst my builder are still around to prep a trench.