The reason I ask is because I (feel) as if I'm making the same sequences of clicks between two shapes and I get several different blends each time. Example attached below. Thanks for your time.
The blend tool is dependent upon the location of your clicks. More specifically the difference in the click location relative to the object being blended.
It's best to click anchors aligned with how you wish the blend to proceed (or simply use the
In your top example, non-relative locations were clicked, such as the top RIGHT corner of the square and the top LEFT corner of the rectangle. This causes a rotation within the blend because the clicks are not in the same relative position to the object being blended to/from.
Note the red dot in the image below... the clicks determine the blend. See how the red dot moves from the upper right quadrant to match the first click location, then blends to rest in the upper left quadrant to match the second click location. This repositioning of the blend location causes the rotation. (There are several ways you could have clicked to create these specific blends, I'm merely providing examples for explanation.)
In your bottom example, two relative positions were clicked, such as the top right corner in the square, then the top right corner in the rectangle. There's no rotation in the blend because the clicks were in the same relative position in relation to the objects being blended.
The clicks in the second image were relative, both in the upper left quadrant of the objects. Therefore the blend merely transposed the shapes without the need to rotate.
Essentially the Blend Tool blends objects from the point of the first click to the point of the second click.