Maxxx, as Cybermonk has pointed out, the object in question is actually only 3 sides and a bottom.  Using a box with taper alone won't be sufficient to create it. Of course you can edit the box to get the shape, but in 3dsmax, you can use the Gengon primitive (located under "Extended Primitives"), and change the number of sides to 3.  Then, you can apply a taper modifier to get the shape.  In the attached image, the gengon primitive is on the left, and the result of the taper modifier on the right.  In fact, that's what I used to get my initial result, except that I also just welded the top point verts together to create the point.

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