I'm back, and here's my secret.....
When you're being lowered in a lock there's almost no water movement inside the lock that would move your boat around. Going down is a piece of cake.
When you're going up and the water enters the lock it comes in through "tainter valves" (google it) and is fed through a series of baffles in the bottom of the lock. The baffles don't extend all the way to the upstream and downstream ends of the lock so as the water is rising the water flows toward each end of the lock. Here's a photo of the baffles...
So, if you are tied toward the upstream end of the lock (as shown below in "A") the water hits the stern of the boat (lots of surface area) and tries to push it forward. You're tied to the bollard that's about the midship point on your boat so that is the pivot point whether you're using one line at your mid-ship cleat or a bow and stern line. Since the boat can't be pushed forward, the push from the water will make the bow of the boat move toward the lock wall. Not fun.
If you are at the downstream end of the lock as the water moves toward the boat it is pushing against the bow. Since there's less surface area for it to push against it doesn't have much force and what force there is gets divided by the bow so the push is almost equal on both sides of the bow. With less force trying to move the bow the boat sits basically stable.
Most boats in the 26'-36' range get by with using one fender aft of the bollard and one or two forward of the bollard. We use two fenders aft and three forward just to be on the safe side. Dealer's choice on how many to use and where to put them.
Here's a photo of what the bollard looks like. FYI, I grade my wife based on how quickly she gets us secured to the bollard. How pretty, or not, her knots are is not a factor. Some of them look like a Gordian Knot but if she is quick about it I don't really care.
So, Tom, there's my big secret for you on how to easily transition a lock. The first round is on you, my friend!