I do not agree with the wording on this text.
"A planar shockwave has advantages: the 'blast' effect of a spherical explosion goes down with the square or the radius (4 Pi r^2). If focused into a planar one, 'blast' goes down with the radius (2Pi r). So if you can aim the shockwave, the mine has a much larger effective range."
4Pi*(r^2) = surface area of a sphere. I think that this person was trying to say that the volume of a sphere (4/3)*Pi*(r^3), from an explosion standpoint, will taper off more quickly than a two-dimensional explosive ring, or cover less distance effectively in any awkward situation when you have to run a legitimate comparison between the two; in either case, what's written currently is difficult to read or make sense of.
I am not well-versed enough in the math regarding falloff of explosions or physics simulation to give an expert opinion, but comparing the surface area of a sphere with a radius of 3, which is (approximately) 113.09733552923255, you'd need a flat circle with a radius of approximately 6 to cover the same area.
If the industry calls this the "Praxis Effect," why not rename the trope to match?