Tomorrows development release will contain a couple of improvements to the drawcall minimizer functionality. The main improvement is that you can now also minimize textures that are repeating. ModelConverterX will repeat those textures for you, before inserting them into the combined texture sheet.

As you can see in the image below, there is a checkbox with which you can tell the minimizer if you want to include the repeating textures or not.

By including repeating textures you can possibly reduce the amount of materials in your object a lot more. But depending on how many times the texture is tiled, it might also result in a much larger texture sheet. So you need to find a balance between those two.