You are correct, in the Northern hemisphere lefthand twist will cause spindrift to lessen coriolis effect, not add to it like righthand twist does. Oposet in the southern hemisphere.My understanding is that a left hand twist in the northern hemisphere will cause spin drift that cancels out the coriolis effect to some extent. Right hand twist does the same in Southern Hemisphere.
But that may be 100% internet BS also.
These values are not huge, but are there. Why not take advantage of using the twist direction to help rather than hurt when ordering a custom barrel?
I like to have as many accuracy enhancements as I can, especially if they don't cost more.