This is a very interesting feedback.
I have been using Festo clear 3mm tubing to protect the antennas from static electricity discharge for a long time. The idea is to avoid any contact between the fuselage/structure fiber surface and the antenna wire. The advanced range test did not show any difference with or without the tubing.
However I did try the black antistatic festo tubing ( ref number PUN3 ). I believe that this tubing is made of a plastic that includes some conductive material and is meant to carry the static electricity away thus avoiding accumulation. The range test was significantly reduced with this. It is a great product for fuel tubing and not for antennas protection...

Did you experience similar results with any specific tubing ? What brand, what color ?
I wonder if some specific plastic pigments could act as a conductor and reduce the antenna reception sensitivity.