Creating reversed double spiral ?

[msh]

I'm looking to create a spiral where:

- The line has a big width (using a 8k img, need around 300 units)

- The width of it is biggest at the center, and gets smaller until 0 at the "outer edge"

 

I tried to use this Spiral Plugin: 

 

 

 

I thought about doing it with the Secondary Color line, and filling between the lines so it will end up like the width I wanted,

but the space between the 2 lines is actually smallest at the center and bigger as it spiral "outside", which is the opposite of what I'm looking for.

 

 

 

[Reptillian]

If there isn't a plugin or filter within plugins, then it needs to be coded. This does not look too hard to do, but wouldn't do it myself.