It's not moving the blast away from the shooter with a longer barrel but allowing the powder more time to burn and that reduces the amount of blast coming out the end of the barrel. So does using a faster powder in magnum pistols.
A longer barrel does move the blast further from the shooters face. It ALSO gives the powder more time to burn, but more burnt powder does not decrease the muzzle blast, it actually produces more gas, but being farther from one's face makes it seem less.
I don't use "faster" powders in magnum loads. The fastest powder I use in those loads is Unique or sometimes Blue Dot. Mostly its 2400, or Win 296 or sometimes AA No 9. I want the slower powders to get the most possible and practical from magnums.
I also want my magnums to be heavy handguns, and don't care about how they might catch on a car seat, as I don't wear them in cars or usually on a belt.
The length of a barrel doesn't usually have as much of an effect on the mechanical accuracy as the quality of the barrel and the load.
Where it does matter is in the "shooter accuracy" with iron sights, mostly but also to a degree with optics, by moving the muzzle farther out, and changing the balance of the gun, along with the additional weight and its recoil reducing properties.
Also keep in mind that the differences resulting from different barrel lengths are only comparable in guns of the same type. With revolvers, there is, to me, a difference in balance and feel between SA and DA types, so comparisons between barrel lengths should be held in each class respectively, and this gets even more important if you include other action types in the discussion.
For example, I have a 6" barrel pistol in 9mm Luger. Accuracy of that gun (groups size) is better than any other 9mm I've ever seen, or shot. I put this down to a good barrel, but mostly to the fact that when that gun fires, nothing moves when the cartridge goes off, or after, until I open the action.
Its a T/C Contender. Shot to shot repeatability in that gun is very precise, more so than any semi auto or revolver with parts moving or multiple chambers. Not saying there isn't a 9mm pistol more accurate than that single shot, but I haven't met one, yet.