By your logic a carpenter building a pitched roof would have to change the angle of each truss where it meets the outside wall as they got farther from the center of the building. The rod holding the stone is simply moving along the plane of the roof as you move it left to right and the angle where it meets the O1 is not changing - just like on a roof where the roof plane meets the outside wall. Your drawing is leading you astray because it mixes up two different views of the triangles in question. First view is the narrower triangle formed by looking down the O1 stock from the end - the tip or the handle of the knife. The second view creating the second triangle with the longer sides is looking at that second triangle also from it side. But that side view is found by looking over the top of the O1 stock from in front of the sharpener somewhere, not down the length of the O1 stock. If you turn the sharpener and look down the O1 from one end or the other while moving the stone along the piece of steel you'll see the stone is always moving in the same plane so making the same angle while contacting the piece of steel. Moving that to your drawing, if you stay in the same view of the triangles, the second larger triangle is actually completely hidden behind the first. You could also see this by laying a board or a piece of cardboard across the steel you are using to simulate a straight cutting edge and lifting it to the angle position you want to sharpen at on the upright. The board or cardboard always makes the same angle as it meets the steel along its full length.

 

Just to clarify a bit. I'm not saying that the 2 triangles in the drawing aren't actual triangles relating to the cutting edge. Both do show something about the angle at the cutting edge. It is just that the sharpening angle is always measured at 90 degrees to the cutting edge, just like the angle of a truss. The second larger triangle is measuring the skew angle of some cut you might be making. The angle you are looking at in your second larger triangle is the effective cutting angle if you are pushing the knife forward and down in the direction the rod is pointing through whatever you are cutting. The effective cutting angle is measured directly in line with the cut direction. This effective cutting angle is lower than the actual sharpening angle in this case. That cutting angle is always lower to or equal to the sharpening angle depending on the direction of your cut. The more forward (or backward) motion you have relative to downward motion the lower your effective cutting angle. If you work with hand planes or chisels you are probably used to skew angles. You sharpen the blade at a set angle and if you cut with the plane oriented so that the cutting edge is 90 degrees to the cut then the cutting angle is a combination of that angle and the bed angle in the case of the plane - or just the sharpened angle in the case of the chisel. You might have trouble cutting pushing straight into the fibers of the wood. If that is the case then if you twist the plane or chisel slightly so that the cutting edge is not at 90 degrees to your cut, the cut will be much easier. That is because in relation to the wood you have effectively lowered the cutting angle. The wood fibers move over more of the bevel than they would have if you were cutting straight into the wood. You are also of course slicing instead of push cutting the fibers which helps too. This is the same of course for a knife on a tomato. Leonard Lee probably has the best explanation (and diagrams) of this I've ever read in the first chapter of his book on sharpening.