Well asked basic question. As far as barrel tensioning goes, so far none of them work to actually tension the barrel because the force it would have to exert to tension the barrel starts at 2 tons of tension force which would not withstand either the barrel mount or the material of the tensioning shroud itself. In many cases, barrel tensioning alone is more detrimental than having a positive effect. A better solution to the poi shift would require the use of a barrel at least 20mm in diameter. As for fx airguns, the construction of the barrel itself when it is made up of several layers there no barrel tensioning system will basically affect anything because you cannot tension the liner itself. However, there is a small modification of the liner-carbon-wrapper connection to improve the poi shift. A good improvement in poi shift is provided by the plenum around the barrel which is offered by the Fx Panthera and its other clones. For these airguns it is ideal to use all available modifications to improve the poi shift and thus improve its accuracy even at high power. The shroud around the barrel performs a basic function and that is the soundproofing that is created when the shot is fired. The second secondary function is to stiffen the barrel. It is not entirely good to tighten the shroud with great force with the idea of helping to improve the poi shift. It doesn't work that way. Rather, you achieve barrel alignment.
