  While string models describe initial state radiation in ultra-relativistic
nuclear collisions well, they mainly differ in their end-point positions of the
strings in spatial rapidity. We present a generic model where wounded
constituents are amended with strings whose both end-point positions fluctuate
and analyze semi-analytically various scenarios of string-end-point
fluctuations. In particular we constrain the different cases to experimental
data on rapidity spectra from collisions at $\sqrt{s_{\rm NN}}=200$~GeV, and
explore their respective two-body correlations, which allows to partially
discriminate the possible solutions.
