Mesh Combine Increases Triangle Count

I've just noticed that I'm getting a significant increase in my mesh triangle count when performing a mesh combine on child objects. I'm seeing a doubling in mesh size. While the reduction in draw calls is helpful, the increased mesh triangle count is completely undoing any benefits and slowing down rendering.

Here is my code:

 #pragma strict
 
 @script RequireComponent(MeshFilter)
 @script RequireComponent(MeshRenderer)
 
 function Start () {
     var meshFilters = GetComponentsInChildren.<MeshFilter>();                        // Get the MeshFilter components of the children
     var combine : CombineInstance[] = new CombineInstance[meshFilters.Length-1];    // Create an array to hold the meshes
     var index = 0;
     for (var i=0;i<meshFilters.Length;i++) {                                        // Create a loop to iterate through the "combine" array
         if (meshFilters[i].sharedMesh == null) continue;
         combine[index].mesh = meshFilters[i].sharedMesh;                            // Assign the mesh of this child to the sharedMesh
         combine[index++].transform = meshFilters[i].transform.localToWorldMatrix;    // Position the mesh
         Destroy(meshFilters[i].renderer);                                            // Remove the renderer as it's no longer needed
         Destroy(meshFilters[i]);                                                    // Remove the mesh filter as it's no longer needed
     }
     
     GetComponent(MeshFilter).mesh = new Mesh();
     GetComponent(MeshFilter).mesh.CombineMeshes(combine);                            // Get the combined mesh
     if(renderer)
         renderer.material = renderer.sharedMaterial;                                // Assign the material
 }

I'm hoping someone can either spot something in my code or offer other assistance. Maybe something to do with the way the fbx files are imported? I've toyed with the normals and tangents, but with no success.

Thanks!