I disagree with the reasoning behind the Base Drag Hack. The reason a flat plate has an effective CP behind the plate is not anything going on in the wake. In the inviscid, irrotational approximation where the computation predicts no wake at all the plate has an effective CP at negative infinity, so wake effects actually bring the CP forward not back. The plate wants to face into the airstream because it generates lift and the center of lift is in front of the geometric center of the plate. It's basically a fin operating at a very high angle of attack.

As a practical matter, it's easy to find cases where the Base Drag Hack gives bad answers.

Consider a spherical rocket. By symmetry a sphere should be neutrally stable, so it's CP is at the geometric center. Here's what the Base Drag Hack says about it:

View attachment 433305
The CP is way too far back.

I'm pretty sure the problem with fat rockets is not about base drag, it's a combination of mishandling the behavior of fat noses and neglecting the effect of body lift.

Also, I really enjoy saying "consider a spherical rocket". Also also, anyone working on aerodynamic modeling of rockets should really run some basic geometries with known behavior (spheres, flat plates, cylinders, cones, etc) through the widget and see what they get.