RE: Vertical Rolls
I cover this in my upcoming video. There are four forces, one which is weather vaning, which I suspect you are feeling. Don't fret, as long as it augers into the wind consistently you are ok. I'll keep you posted on the video status. Shooting for a winter release. It should be good.
If its a perfectly calm day and the plane is consistently doing it (you have to pull up in to a vertical up line entering from right to left and then from left to right) if the thrust, rudder and elevator trim is correct, then what is left is aileron differential. As long as you have adequate thrust to weight ratio (where the plane is not slowing down significantly at the top of lines) the vertical CG should not influence vertical up lines significantly.
The best desription on differential I've seen on this subject is from Peter Goldsmith. I can't recall if it was a Model Aviation magazine article or in the Diamante instruction manual (which has an excellent trimming and flying section I might add).