Hello,
"Of course, I created different sizes"- I don't know what you mean but it's not LOD of different sizes,
LOD is Level of detail no sizes of models but - Each model has a different number of polygons/vertices and different size of textures, for example your ship 1.lod 5000 polys,1024x1024 texture,
2.lod 2500 polys, 512x512 texture
and 3.lod 1000 polys and 256x256 texture
....no sizes ....polygons
maybe show some image with issue....hope this helps :)
p.s. in Blender you can use Decimate modifier for each LOD level and tweak models if necessary