Dani,
I think you may be missing a piece of the puzzle - It's not type specific, it depends on how the aircraft is loaded.
In a conventional wing & tail config, you're only likely to see tail download towards the rear extreme of the allowable COG - depending on the aircrafts aerodynamic stability the most aft allowable COG might not be far enough back to produce tail download.
I'm reasonably sure that at most forward COG, EVERY a/c will have the tail producing lift downwards - i.e. upload on the tail.
I also think the sailplane thing is a red herring - flown them a fair bit. I'm quite sure (from memory) that the duo discus (for example) has a 'inverted' section on the tailfeathers.