I realise that it is difficult to get scale of such a diagram but it does look as though "Cornwall" was far, too far away, from the boarding party to provide any form of support whatsoever, in which case the helo should have been ordered to stay in visual contact and not despatched on other surveillence work.

Not surprisingly I'd tend to believe that the boats were taken inside Iraqi territorial waters, the ship they had just searched was, after all, headed for an Iraqi Port, Umm Qasr or Basra, taking into account the position of the nearest headland in relation to where it was going what would it be doing in Iranian waters?