That’s really a hack on the wording of the rules. You’re not allowed to cup more than an 1.25" into the end of the bat (rule 3.02(b)).
But tapering? You can go 4 inches down the barrel and it’s fair game. Your contact area isn’t as good but the weighting effect is the same.
What do you mean the contact area isn’t good? The article indicates that since you are increasing the size of the bat in the area that the hitter most often hits, leading me to believe they are custom making for a particular battery’s swing, it’s more likely he’ll hit it since it’s wider there.
The maximum barrel diameter is 2.61 inches. On a standard bat, it’s full-diameter after the handle all the way to the tip. This maximises the area you can hit the ball with.
A torpedo bat can still only be 2.61 inches at the widest part. This means less barrel diameter towards the tip. So, a smaller contact area.
