I go one more..

With Autocad, I draw an ellipse about the rigtht size, chop in half, then plot it out (1:1) onto cardboard, and use that as my 'template'. Resize (rescale) the ellispse as needed..

The nice thing about an ellipse, is that the mid points; the 'quadrant points' will be 'tangent' to the sides of teh fuse, and blend nicely to teh built-up box fuse.

(The parabola you've posted looks like it starts off already at an agle, and in my opinion, would look funny. No smooth transition from vertical flat to curvy..)

just my $0.02 worth....