Frei Otto wet thread definition problems

I've tried to write a wet thread clustering definition to cluster lines from a set of box corners to surfaces above and below, but I'm having a bit of trouble with the threads blowing out rather than clustering as I'd hoped. I've used Daniel Piker's definition from another thread (http://www.grasshopper3d.com/forum/topics/frei-otto-wollythreads-ha...) as a start, but I've either done something wrong or got the force levels wrong. Can anyone give me some advice on how to get my lines to cluster nicely?

Regards,

Sean