I'm not too familiar with the slightly smaller pattern planes, but am I right in thinking that it's a Sebart ARF?
Just asking, because from what you're saying, it does sound like an issue with (probably) too little positive incidence on the wing,relative to the tail.
A club colleague,who is thorough in such things, has/had(not sure which) one of the smaller Sebart Angel S models (S50?),which initially needed a lot of up elevator trim to fly level,and,although I don't recall the numbers, it had negative wing incidence as assembled out of the box.
He did actually hack it about,to get some positive onto the wing-and of course the need for up elevator trim went away.
To give Sebart their due, (I believe Seba himself sanctioned it),the UK distributors did supply another one FOC.