Yes & No Chris,
I set it up at 45deg and milled 2mm off the corner (about right for the designed 5mm rad).
Got the small 12mm wide fine file on it and
just took off the two corners left.
Then a small Swiss file that was still wide enough to bridge the gaps and blended them together.
I must admit I was dreading it in-case I made a right mess but it went ok. I think less is more with filing radii just take off the corners gently and before you know it there's a curve, Haven't a clue if it's the right radius and I'm never going to measure it in case I'm tempted to go back at it with a file.
finished up with 600 then 1000 grit dry so far, as with the rest.
Cheers.

Steve.