Issue with Modeling Eyebrow Hair

I’m trying to use a texture to influence the density of the eyebrows on my character.

When the emission number is 1000, I see no hair. When I increase the emission number to 40,000, I see around 10 hairs on each eyebrow.

When I increase the emission number to 50,000, I see around 5 hairs on one of the eyebrow and none on the other.

When I increase the emission number to 100,000, I see no hairs.

Does someone know how to reliably get a good number of guide hairs for my character’s eyebrows?

Additionally, does anyone know the relationship between the “Hair Length” under the “Emission” tab of the Particle properties and “Normal” under “Emitter Geometry” under the “Velocity” tab of the Particle properties? They seem to be related, but they are not the same.

Thank you in advance!

Using a black and white mask for hair density almost always require you to first limit the initial emission of hair using a vertex group. If you don’t what is happening is that you emit 1000 hairs, they are placed randomly over the entire mesh, with very few in the eyebrow area. So just create a new vertex group and make sure to include verts that belong to faces just outside your mask, and then use that for density in the main particle system, and then your mask will be used effectively to mask out those few extra hairs.