Fascinating discussion
We are very fortunate indeed to have Mmmayday38 contributing here - and it's very gutsy of him to actually spell out what happened and how he felt so frankly and in such detail. It's a real privilege to read his comments. Hats off to him.
We know that when the flap settings were changed by Mmmayday38 (at 240 feet) the autopilot was still engaged - so perhaps the move to Flaps 25 prompted the system to just tweak something somewhere to give the 777 just that tiny bit less drag to stretch the glide and gain those crucial extra yards.
Once the AP was disconnected though it was all down to human skill. ...But phew - it was right on the margin!