Gents, my experience with the Sinking AFS Gen 1 vs. Gen 2 led me to a working calculation that works for me (and perhaps for you too
Find the Rear Half Weight (RHW) of an existing head that loads the rod properly. Incidentally, this RHW calculates differently between sinking heads and Floating heads due to a leader effect.
I found that approximately the same RHW for any heads* feels like the same load casting, keeping in mind that the calculation must consider leader effect for floating heads.
For example on my Zpey HM Signature 13' 1" 8/9 rod, I casted a Guideline 3D I-2-4 sink in 8/9 weight in 44 feet.
The RHW for this 8/9 line was 353 grains. But I wanted a shorter head for tighter casting conditions.
I went to Guidelines calculator and found that the RHW of the 10/11 class was around 366 grains for 39 feet, close enough to the above 353 grains.
I am now casting Beulah's Aero Head in 7/8 (510 grains) on the same rod for Summer Run steelhead. Have yet to do the calculations to confirm this.
However, my blog on my website (footnote) contains in depth explanation and calculations based on Zpey 12'4" 7 weight rod, covering AFS floater, AFS Sink Gen 1, and the dubious AFS Sink Gen 2.
Hope this can help.