I suppose this is a no-solution question but is there a way to know the best value of extrude and ray distance while baking a normal map from low poly to high poly model?
For a really good bake, you can use a Cage object.
Hit the Bake > Selected To Active > Cage checkbox. Now you can choose a Cage object.
During the bake, rays are projected from the cage object to the mesh.
To create a cage, duplicate your mesh, scale it a bit bigger along the normals (ALT-S), and then edit it manually from there.
This gives you much more control than using the Extrusion value, which just generates a cage object automatically.
The Extrusion value makes the ray begin before the baking surface. The Extrusion value that you need to choose will depend on how much (in scene units) the object you need to bake go through the object that bakes (by the way, make sure that you've applied the scale of the baking object). Here I represent the distance with this green line, just choose a distance that will be a little bit more than that, this way the ray will begin before the surface of the face and therefore will be able to catch this surface:
Or create a cage as suggested by Samuel Sullins.
As for the Distance value, which is the maximum distance that you want the ray to go, just keep it at 0 (which actually means no maximum), unless you have good reason to stop the ray at a certain distance?