I agree with Doug above. it is not always possible to get the trailer exactly level because of different hitch heights, trailer coupler heights, truck hitch heights etc, etc. etc. so rather than set it up with the tongue a little bit high, it is better to have the tongue a bit low.
6 inches would be a huge extreme and would most likely have the WD bars hitting the ground often. It would also overload the front axle of the trailer a lot and possibly cause a blowout. Remember, an inch low at the front equals almost an inch high at the rear for a two inch difference. That slant would be noticeable.
I think most consider an inch or less as "slightly" if you can't get it level. If it looks level then it most likely is close. :)
Barney