Ross, here is something that might help with fading out the diameter of the BB's:
Here is a normal BB core. On the picture you can see that I have made a constrictor knot at the end. I always take a needle, pass the thread through the core and then make a constrictor knot since it is more secure and it wont slide.
Add another strand to the core. I works very good when you feed the needed lenght
into the corestrand, but it should also work when sliding the needed length over the core. Dont forget to sew the 2 cords together
securely.
If you choose to feed the added strand
inside the core, don't make a constrictor knot before feeding in the additional strand.
Feed the addtional strand in right where the BB's end.
About the lenght of the additional strand - it depends on your drop incements. The picture above shows roughly how I would arrange the plaitcount aroud the core: For a BB loaded core, I wouldn't go lower than 6 plait. Carry out the 6 plait over the 2 (green and orange) core strands after the BB's end. Then drop to 5 plait (over 2 corestrands) and let the additional strand fade out in the middle of the 5 plait section. The second half of the 5 plait section will be over one empty strand and then drop to 4 plait.
This is not a given measurement (especialy not the measurements on the paper). 4 plait over 2 strands also works, but if I can avoid it in the core, I preffer doing a 4 plait over 1 strand.
Ben