I think that area is important enough to spend more than 4 blocks on, I normally spend 6 on that area, to provide sslightly layered vertical blocks and an attack ramp. (Screenies in a few minutes)
EDIT:
I wouldn't normally put an entrance there, it makes you vulnerable to snipers and rocketeers while you are using the health and armour chargers. (I used 7 here for the sake of double layering the wall.)