I'm a bit late to the party on this one but yes - I also use a relatively narrow straight beam (1"/25mm). It makes it easier to keep straight and, as I move progressively across the width of the fretboard, I can keep tangential to the curve of the frets better. The metal filings you can see as you are sanding also give a good gauge to any lines missed and the general progress towards flatness.
What I do do, however, is finish off with a standard radius block with some emery to smooth out any facets I may have left across the width of the frets.
Finally, I use the same radius block pushed across the frets (so doing 3-4 at a time) to get the starting sanded 'grain' direction on the frets the same as that of the subsequent re-crowning/polishing.