It was for all frets.
The nut, when the kit arrived, was very high, so I sanded it down a bit (which made a massive change for the better - just left a bit of fret buzz) I made the adjustment based on the height of the nut on my telecaster (Jet brand). I may have sanded the low E side a hair too low - but the nut is still just over a millimetre higher from the fretboard than the nut on my telecaster.
I've levelled the frets, adjusted the "relief" and the bridge saddle height but it took a bit to get rid of the buzz - which has gone mostly, if the string is plucked "with vigour" there is still a bit.
The "action" is now possibly a bit high, I do tend to "catch" that string when "I help my daughter" (it seems the more I practice the better she gets - of course, she thinks it's her!) but obviously if I lower it I run into the fretbuzz again.
This has made me think that if the fretboard was a bit lower (if the neck socket a tiny bit deeper (no more than a mil or so) that might be the cause - and I can lower the saddle height/action just a tad.
Otherwise it's working rather well acoustically (it's not wired yet), a touch "twangy" and high pitched and to my ear a bit louder than expected - but I'm putting that down to the Douglas Fir, the 24.75" scale length and the lighter strings (9's).