The problem is the Dolphins defense was playing man coverage and Henne has always been good against man coverage. Henne just can't read defenses unless it's man-to-man. But even a 6 year old can read man-to-man.
Henne can't read any other D. All a defense has to do is mix their coverages and disguise presnap in cover 3, cover 2, or quarters coverage etc (or ANY type of zone coverages) and Henne and the dolphins offense are screwed
Other teams already know that henne sucks against any other defense, and that's why it was so rare for henne to see man defense after the first few games last season.
That's also why Henne looks decent against the blitz. Because the defensive backfield is in man coverage a large majority of the time when they send extra people.
Only the raiders were stupid enough later last season to play man 2 man exclusively throughout the game. Notice that as soon as they switched up to a zone for a couple of plays Henne was confused and threw a horrible ill advised pass to the middle of the field at the goal line for an easy INT with 3 Raiders around the ball with no Dolphin player in sight.. Of course, the Raiders then went back to man coverage after that for the most part -- they;re the raiders and they're stupid.
Do you remember a couple of years ago when Henne had like 16 straight completions against Jacksonville on the road? He was just one shy of the franchise record set by Griese. Well all those Henne completions were against man coverage that day. As soon as the Jags switched up to some zone looks in the 2nd half for the most part, Henne was lost, the dolphins relinquished their lead, henne threw INT's and made some horrible passes missing wide and away, and the dolphins were lucky to escape that game via the defense making some huge plays and the running game taking a bit of time off the clock. But Henne was awful later on with the zones.. and this has been a constant with him over the past 3 seasons.
The book is out on Henne and how to easily confuse and fluster him. The rest of the NFL has it down. Only with the rare exceptions like the Raiders ( and their stupidity as an organization along with injuries to Nnamdi and their 3rd DB that day) can Henne get a free ride to look better than he is.
In other words, don't get your hopes up over a couple of practices when Henne was facing man coverage. He won;t see those coverages in the regular season. The coaching staff probably decided to go to man coverage for a few days to raise his confidence level and take the Heat away from the "Orton chants", and all the anti-Henne stuff in the media. But that's about it. Don't look too deeply into this.