There are two major things that affect accuracy when it comes to sabots, granting that we have excellent sabots that are capable of doing the job they are designed for well.
First: the reason there is a wide range of thickness available in today's sabots is that the barrel makers for muzzle loaders are not only using gigantic tolerances different brands have different starting points. There for you have to find the right thickness for your particular gun.
Secondly: I have found that even when the sabots are the right thickness as an example the SBH, the 300+ Harvester and the MMP HPH24 are all the same thickness and all fit my TC guns and yet to maintain the level of accuracy I want I have to use the SBH with certain bullets the 300+ with certain bullets and the HPH24 gives best accuracy with a few and I have to change the length of some for certain bullets.
I believe that the wind off the nose of the bullet affects the way the sabot comes off the bullet and if it does not come off strait and bumps the bullet or drags down one side then the accuracy is affected. Lee