Thanks rccpgm what you are saying makes sense and i'm now thinking is the case, but i cant find anything from juniper to state that though. The closest i can find is the below but its not in refernce to EX hardware, from 2012 and it is stating fixed 3bit.
"The algorithm used by the router for forwarding over a LAG bundle might cause a distribution of the traffic that is less then equal. The algorithm operates by creating eight bins, numbered 0-7. There are always eight bins, regardless of the number of interfaces in the bundle. The eight bins are distributed across the links based on an L2 channel algorithm. Each link is allocated to one of the eight bins. When one of the links in the LAG bundle fails, the traffic at that point is not equally distributed across the member links. Whenever an odd number of links are present in a LAG interface, such an imbalanced distribution occurs.