Hi David
This issue of a profile fuselage twisting in flight has been beaten to death over the years and if you read the volumes of posts on here regarding this, the remarks all always the same and the discussion gets quite tiring and boring and no magic solution is ever found. It is a profile and a profile is a profile and there are thousands of them out there going around in circles and bringing a lot of joy to a lot of fliers. Ty and some of the other guys are right, it is a great flying profile. When Brodak still made the ARF profile Pathfinder, I bought one and flew the Hell out of it and it flew great until it met its ultimate demise called pilot error. Seems all of my models eventually meet that fate. My advice is to not worry about the tail flexing a little, it aint going to fall out of the air because of this and you will enjoy flying it.
Mike