Hi Mick,
you have to specify in each action the following attributes:
ForEach, which have the IEnumerable instance.
CurrentInputName, which will have the current object in the iteration.
and the IterationGroup, in case that you want togroup the iteration.
regarding your question, you should specify the CurrentInputName wich will have the name of the action input property where the value that will be set.
maybe you have to modify your IEnumerable argument to do that.
hth.
jose.