I'm one who also put the antenna higher up in the vertical stab. There have been a couple people who have done this and reported good performance and let's face it - a dipole antenna is a good tried and true antenna with excellent performance. My first question would be how are you going to secure the lower pole of your antenna that is down with the trim motor and rudder cables? I would be leery of having things around where my control interfaces and parts that move are located. John McBean saw my install and asked me about what my plan was to access the antenna if I ran into issues later. My answer was simple. I'm leaving the 'normal' position on the aircraft open for an external antenna open so that if the antenna I'm using has issues, I'll cut the cable off at the top of the tail access and re-route it to the 'new' antenna location. I also agree with Eric's comments on testing methods/results and such. (I measured my VSWR with a network analyzer Eric and it came in at about 1.7:1. and think you are correct that the mismatch will get better with the longer cable. 2:1 is about 10% reflected power and that longer cable will help)

Gary