Best Way to Fret Level with a Bowed Fretboard

[PSmill]

I have a 40 year old classical guitar, it's in great shape structurally, although a working guitar with lots of wear. The owner complains of isolated frets intonating flat on few frets here and there up and the fretboard, on the treble strings. I see no obvious cause of this, other than the frets are showing wear, small dimples, a half dozen high frets, with high spots mostly in the middle of the fretboard (D, G, B strings), from fret 3 to 10.

The action is good. Saddle, bridge, and nut no obvious issues.

I'm going to suggest a fret level, as it's due in any case, any may, or may not, resolve the issue. The isolated location of the issue suggest is may be fret specific or specific to a region within the neck.

The fretboard has 0.012" relief while string up, and with string tension released 0.008".

What is the best way to level the frets if there is 0.008" relief in the neck? Using a short 5-6" levelling bar and working small areas at a time from the heel up towards the nut?

thanks