Does the position of the Ferrite bead matter?
My answer hopefully applies to beads but also ferrite clamps on cables.

If it's preventing susceptibility problems due to interference coming down a cable then its position is not that critical. However, if it's stopping emissions getting out from a device, a better position is as close to the interfering source as possible. There is every chance that interference getting onto a cable (such as from a switched mode power converter) can radiate from the cable so, best to keep the ferrite up as close to the source of noise as much as possible.