The only time volume should not work would be when there is no volume (according to Blender), so if there is a hole anywhere on the object (or if it is a plane/something with no thickness) no matter how insignificant it may be, then Blender says there is no volume. I've had the problem while I was doing my fluids tutorial. If you know it has no holes and it does have a volume, then there is probably something completely different going wrong.
As for the distance from the shell, that is something I have never figured out. Sometimes it seems OK, and sometimes it does not. Even in the tutorial there is a considerable distance from the obstacle. Raising the resolution tends to make it better if I remember correctly, but it doesn't exactly fix the problem sometimes. Technically, you will never touch the object, but it should get close. I think the size of the scene will also effect how close the fluids will be to the object.
In any case, I don't think the fluids system in Blender is the greatest. There are some things that pretty much everyone has problems with (such as that gap problem). I tend to avoid using now, because of how slow things go with it and how hard it is to get things just right. I'm just not patient enough.