Tithing, Net or Gross?

Here's an update on this post on my Faith blog:
I've been pondering lately the historical meanings of the words "increase," "gain," and "surplus" and am finding it very difficult not to conclude that they mean "income after all paid expenses." It's very likely that tradition has developed in a way that most Saints pay too much in tithing and not enough fast offerings and private giving. I have decided to experiment with the amount I give officially and unofficially in the coming year and to gauge accordingly the consequences.