Hi Burr, actually it does work like that so you may like to use the value in that way.

For example here is one with Rho = 0.5 :


And here Rho = 0.6 :


And here Rho = 0.8 :



As the value moves towards 0 it becomes flatter, here is Rho = 0.01 :



The category of conic section is also related to the Rho value.

With Rho = 0.5, the curve is a segment of a parabola.

With Rho > 0.5 and < 1, the curve is a segment of a hyperbola.

With Rho < 0.5, the curve is a segment of an ellipse.

- Michael