Swarming Tactics

I have a very hard time understanding how and why HMS Cornwall, with the task force commander embarked, allowed her boats to be surrounded or cut off from herself. My understanding, from a former trainer of Canadian naval boarding parties, is that our protocol is that the frigate or mother ship always ensures a clear unobstructed route is maintained and the boarding party boats are never cut off. This would require Cornwall to manoeuvre to intercept the Iranian boats or provide cover to her boarding party. Obviously, this was not done.