You might try a space between the numbers..say 0 8 6 9.
It could just be that at .050 high lettering and a cut depth of .005 they just run together.
So you could try a slightly bigger letter height and the same depth of cut or same height and a smaller depth of cut.
Also the size of the ball mill or the size of flat on the end of your engraving tool could be contributing to the problem.
By that I mean if you where to use a 1/2" ball end mill at those setting you would just get a mess of lines instead of clean lettering.