That second control lever one typ associates with a draft control doesn't function as a normal draft control which attempts to control implement depth by sensing change in force exerted on the 3pt links.
On the Yanmar's I'm familiar with, this control attempts to do the same thing in a different way and only for yanmar tillers set up to work with the UFO controls. There is a arm near the upper 3pt arms and it is linked to the tiller's drag via cable and some linkage. The draft attemps to control the tiller depth by associating the angle of the drag with tiller depth.
From several others that are much more in the know than I am, I've been told I'm the only one they know of that has ever hooked up the UFO controls to control tiller depth and side-side angle of the tiller.
See pics. 1st shows the arm associated with the draft control. There is a cable attached which runs back to the tiller. From there, pic 2, there is some linkage to the drag.
When connected, I can manually lift/lower the drag by hand and the 3pt reacts by either lifting or lowering the 3pt arms.