Slope floor to create tension in wood
Flat is an option. 

I'm not altogether clear on what scheme you think you were following, or what you think it was doing for you, but it sounds suspiciously like something someone dreamed up and presented as fact, with a dubious or non-existant basis in reality. A slope does not "create tension." A load does that.

Buildings on post foundations are made with level floors all the time. If the posts are set properly, the buildings don't "move and crack" either. If your posts are heaving, they were not set properly...