Reefing lines for FS

Hello all, 
Our fleet of Flying Scots are equipt with Intensity Sails.
I want to replace some of the reefing lines but wanted to know what most FS use.
I wrote to Intensity Sails and so far they said a 6mm line should do the trick but I cannot get how much reefing line I should use for each when reefed in the following manner:
lower the mainsail to the reefing grommets and tie reefin knots loosley underneath.
I am looking for the manuf. suggested length of 6mm or BEST PRACTIVE out there.

Intensity should be able to tell you based on their design.  I would imagine the number and position of grommets matters.