An event instrument will always behave asynchronously, meaning when the instrument is triggered it will play from the beginning to the end (unless Cut is enabled) regardless of where the playback position is on the timeline. Event instruments will trigger referenced events to start playing, the same way as if you were just to press Play on those events and leave them alone.
The playback position on the event instrument does not interact with the playback position on the parent event. You can resize the event instrument by right clicking on the instrument and selecting “Resize to the contents length” which will make it an almost 1:1 scale with the parent event.
For more information on event instruments and referenced events please see our docs.