with top-hinged ailerons a negative differential is needed actually - more down than up!
I know that that’s what is usually stated, but I think it’s worth keeping an open mind until having flown the individual model.
I’ve just flown my new Abbra a couple of times, and obviously it’s early days, but on doing my usual differential test( climb at 30--45 degrees, multiple aileron rolls), there is an obvious yaw in the opposite direction to the roll. To my way of thinking, this implies that the down-going aileron is dragging more than the upgoing one, and so it looks as though the Abbra will need more up ail than down, in spite of its top hinges.