One trick I've heard for estimating the width of tablet weaving is to twist the 4 strands together and then wrap this around a ruler one time per number of tablets that one will be using. Perhaps since this is a round cord, you should try twisting 12 strands of the warp silk together and see if it is too thick for your purposes?

Will you be turning all in one direction or back and forth (ie 4 forward and 4 back)?