I really don't understand the whole enclosure concept. The enclosure definitely makes it easier to capture a field for two reasons. The first reason is that the enclosure forms a sort of pseudo womb and during attacks, tanks are reluctant to leave the protection. Therefore an attacker only need set up a few key strike points, a poorly staffed VH is easily manageable from the 17lb mount and the tanker can move around to avoid providing a set up shot. The tanks will stay contained and troops may be run with confidence. Alternatively, an attacker can enter the kill box and set up for a camping shot that is highly protected from both auto and manned guns.
The second reason that enclosures facilitate attacks is by removing the direct line-of-sight from VH to map room. It used to be maddening to watch the M3 cross the plaza, knowing they were also watching from the tower and waiting to spring a wirb or something just as the M3 goes by the VH, maybe a couple tanks to keep kilroy busy plus a jeep - I have seen it all. Storch pilots, that's my favorite, that trick works exactly once. Anyway, that's all a thing of the past.
As an attacker, I LOVE the barriers, as a defender, I wish we had not been saddled with them. Now, when you see bombers approaching a field, you know you will have to stop and reverse your wirble, not once, but twice as those bombers are bearing down on that kill box. Don't even mention vulchers, you are totally protected from them and they you, while inside the enclosure.
That is why I do not understand them, because I was given to understand that they were added as a response to camped VH's, an activity they seem to augment.