I'm not surprised that in exercising mastery of clip-and-comment that the previous poster left this out from my post:
Originally Posted by DemostiX
How long the bury? That is hard to know without trial. But, I would start with a buried section of smaller line as long as you would make it if the line were the size of the sleeve.
Plain enough language. Since the cordage in the sleeve is larger than that of the bury, the starting point I suggested is conservative, a longer length, and then it is just a starting point.
It would not be hard for someone regularly working with cordage to bury a piece of say Dynaglide with nominal diameter of 2mm or ZingIt of 1.75mm within another length of 1/8" (3mm) Amsteel blue. How long the bury? 72 x 3mm =216mm, about 8 1/2", whether with Zingit or Dynaglide. Stitch to keep it from slipping, and apply an increasing load approaching breaking strength line, in line with the splice. Record the load at which there is failure, and whether by slippage or breakage. If by breakage, then the bury was long enough. If by slippage, increase the bury. That's what the word trial means.
Quality polyester fiber and the cordage made of it averages about 1/3 the strength of Dyneema / Spectra /UHMWPE weight for weight. Sure, there's variation for quality and braiding characteristics. But, for figure of merit, 1/2 is too large and 1/4 doesn't credit polyester enough.