Physics, ropes and a problem with distance between joints

Hello

I have a problem with physics behaviour and i hope someone will be able to help me

I created two ropes (thanks to a method by R0j0) and attached the last part of the ropes to a sprite but it's really not working as i expected...

Here is the capx, you'll understand what i mean...

https://dl.dropboxusercontent.com/u/5129970/constructforum/rope%20panel.capx

Thanks

up thanks