Pylkkänen's argument is based on the following assumption about how event semantics are computed: when the lower caused eventuality is existentially closed, eventuality modifiers adjoined to CauseP can modify only the higher causing event introduced by the Cause-head.
lower modification of the caused eventuality by verbal modifiers is simply impossible in (3a), and this is an immediate consequence of the structure, given that there are no verbal projections below the Cause-head.