I have to say I am appalled that so many members move inappropriately, at the wrong time of the over and this undoubtedly upsets the batsmen and his concentration. Bearing in mind most of the championship matches are played that Pavilion side of the square, and often in line with the River Stand.
It wouldn't affect T20 matches as those pitches are often on the batsmen friendly wickets on the older part of the square further away from the River Stand and not in line.
I must say the worst place in the country for people moving at the wrong time is undoubtedly The Oval who are most inconsiderate indeed.
With so much available seating at Chelmsford and especially in the adjacent stands I feel somewhat supportive of this move. They always close the seating at Worcester, Northampton, and many other grounds when there is seating behind the arm.