flemish 'string jigs' are merely aids to help a process that is as subjective and unique as the people twisting such strings up.
they're just a guide, no more or less.
the master string makers, and we have more than a few here at trad gang, can build flemish twist strings as readily and easily as a concert pianist can bang out a mozart sonata whilst i and others are still struggling with 'mary had a little lamb'.
you need to pay yer dues, and build a LOT of twisty bowstrings, to become accurate enuf to twist up a flemish string of the correct length for a given bow length and brace height on the first try.
until then, keep twistin' the night away! :D