Sampling point size of 10 is way too small. Padding of 5 for sampling of 10 for a ratio of 50% is too large.
A good target Sampling point size is between 72 to 100. The default is 90 for dynamic font assets. The padding should be 10% of the sampling point size or in the default case 9. So target Sampling of 90 with padding of 9.
The atlas texture size is a function of the number of glyphs you are trying to fit in it. Typically 1024 x 1024 is good.
See the following video about the Dynamic System. See the links to the Font Asset Creation video and Working with Material Presets in the following sticky thread .