I remember what it was now.
With the prewar 6x9 cameras, there are three distance settings: Close, middle and infinity.
You will get the sharpest photos, if you set the lens to the middle distance. When I set it at infinity, the photos were soft. But when set at the middle distance, the photos were sharper. For closeups, go ahead and set to the close setting.
I noticed this oddity when I was checking the collimation of the camera. Yes, a box camera. I noticed that when I set the lens at the middle distance, it appeared to be a bit sharper than when set at infinity. So I set out to prove whether this was the case, and it was true.
This appeared to be the case for all of the Box Tengors that I encountered that offered distance settings. The very early cameras don't offer that option.
For the postwar camera with the coated lens, use the distance settings as you normally would.
By the way, I see a Tengoflex sold on eBay recently (early 2014) for US$700.
Here are two photos to show what I mean. You can see how the infinity setting is softer.
The middle distance offered better depth of field, too. Look at the parking meter and the buildings in the distance.
Left photo: Lens set to middle distance
Right photo: Lens set to infinity