I see. If you want to control the outcome of a meshing, you need to set the MeshingParameters and obtain a mesh with those. The following code snippet should tell you more. The values do not really make sense, you need to tune these to your case.
The comments show the name of the parameter in the Mesh dialog (use the Mesh command then click “Detailed Controls”).
MeshingParameters mp = new MeshingParameters();
mp.RelativeTolerance = 0; // Density
mp.GridAngle = RhinoMath.ToRadians(5); // maximum angle
mp.GridAspectRation = 3; // Maximum aspect ratio
mp.MinimumEdgeLength = 1; // Minimum Edge Length
mp.MaximumEdgeLength = 5; // Maximum Edge Length
mp.Tolerance = 0.1; // Max distance, edge to surface
mp.GridMinCount = 50; // Minimum initial grid quads
mp.RefineGrid = true; // Refine grid
mp.JaggedSeams = false; // jagged seams
mp.SimplePlanes = true; // simple planes
Brep b; // a (poly)surface defined elsewhere
Mesh[] m = Mesh.CreateFromBrep(b, mp); //creates the mesh(es) from the brep