[EdZ]

In addition to extensor action, you may want to work on drills exagerating 'full roll' of the left forearm. Often the instinct to get 'shut' at the top comes from not knowing/trusting/executing full roll - at least for a swingers motion.

There are a lot of great aids that teach this feel. The figure 8 strap is really the best IMO (assuming a flat left wrist), but if you are not able to 'get' the roll, you might try something like the 'protater' or the 'pure swing', both of which do an excellent job of teaching the proper feels on the downswing.

Getting the feel of the roll will allow you to not 'try' to keep the face square going back, or to over arch, which will let you move away from that shut position

If you are a hitter however, you 'can' play quite well from that shut position.

Just don't confuse the hitter's move with the swingers (in general, angled hinge vs horizontal hinge - or to simplify, a 'no roll' feel vs a 'full roll' feel).