The following picture (link provided) clearly shows the position of the cleats that are used to secure the Valiant with two lines at the stern of Splendour.
You can see that to secure a dinghy with these lines all one needs to do is stand on the rear deck and adjust as needed at the corners. Not
from the swim step. You don't go on the swim step to secure these lines.
You can also see that if someone as short as Natalie would even try to adjust these lines from the swim step she would have to reach over her head to do so and do it nearly blind because of the height and positioning of the cleats from the level of the swim step. Wagner's statement of "We believe she slipped and fell off the boat trying to secure a noisy dinghy" seems at the very least, questionable. A competent investigator would have asked the question.
The other thing this picture shows is just how close Dennis was to the two of them when their argument was carried out to the rear deck, he is a scant few feet away and in perfect eye and earshot of everything that would have transpired on that deck. He told us what he saw, he told us what he heard.