Since this is a 3D game, you have 3 dimensions: X, Y and Z.
The restriction limit seems to be 3 foundations… but only along the X and Y axes…
You can still place bombs 347856348756348765 meters BELOW or ABOVE you, along the Z axis.
Whoever “wrote” the range limit code, is a total idiot. I am sorry to say this, but it’s the truth. It’s a simple vector length comparison…