In short what I explained was:
I had poor latency on Sky. That was due to high Interleaving settings.
BT blamed Sky, not me. There connection was no better. I wasn't happy paying more for something they said they could improve and didn't. In response they tried fast path. That is when the line became erratic and had to be reverted to interleaved.
My whole point was that BT should have known that they couldn't realitically improve latency on a 6km line and shouldn't have blamed Sky's equipment. That is all there in the thread.
You were being contradictory for some unknown reason. I thought it was obvious that long lines didn't handle fast path very well. I thought that was why Interleaving was adopted.
Knowing how it works is completely different to understanding how it works.