I've always found it difficult if not impossible to get the fret ends dressed consistently when they are attached to the fingerboard.
So for this last guitar I bought a fret vice from Luthiers Cool Tools and dressed them all before installing.
The vice cost $15 but you could easily make one in about 15 minutes.

Firstly measure and cut all of the frets and nip out the tangs the required distance.
Turn the fret vice upside down so that the tang is facing up.
Round the end of the fret with a wide file.
Turn the fret back over and round the top of the fret ends to your desired shape.
Polish with sandpaper starting at 600. I finished them up to 12000 micromesh.
Measure your fret and repeat at the other end.
If you make one too short, set it aside and use it on a narrower part of the neck.
And it should turn out something like this.

If anyone would like some more detailed pics of the fret vice I'll post them up next week.
Cheers
Bob