I think the display line is fine where it has been for the past few years;if it did get moved further out to sea there wouldn`t be any point in having the show.
 As it stands the display line is really only an issue for the fast jets,ie the Typhoon and Hawk. 
The Red Arrows are allowed to fly over the crowdline to commence their show,and as there is normally a fairly powerful on shore breeze,some of the formations may overfly the cliffs very slightly.
I understand the CAA have a display supervisor at all airshows and the only incident that I have heard about was that Gerry Humphries pilot of the RV7 got told off for flying too close to the cliffs at Ramore.
He disputed he did anything wrong as he was above the height of the cliffs and flying straight and level with a fair amount of flap.
I was at Bellarena the day after the show and overheard the conversation. 
