Personally, I never had success with coco-coals til I started using a Lotus Bowl. I think the main difference is having something on top to keep the heat in.
If you use foil, you probably just need to make a good incubator for the coals.
Also, are you lighting both sides of the coals? I might be wrong on this front, but I light my coals on a hot plate, heat til one side is red, repeat, then apply.
Hope at least one of the things I mentioned helped you out.