I was simply pointing out that Fastpath and G.INP would both see a 8ms drop in latency and a similar increase in sync.
There's no reason it couldn't be fastpath, just because your line has always been Interleaved.
Lines start Interleaved and many stay that way.
If the line was rock solid why is it interleaved for over a year without ever trying fastpath?
It in no way means it's "gotta be" G.INP.
Given the small numbers reporting G.INP active and nobody else on Sky reporting it yet, it's more than likely not, but it could be, or not.
Without a modem that tells you for definite, or confirmation of the line profile, there's no way to tell either way.
No old HG612 lying around?
Would be good to get confirmation Sky are part of this trial.