Aspect Modification occurs when an any object, living or otherwise passes through a window whose other end is of a different aspect ratio. This can be used to grow or shrink the object's height or width, depending on the ratio when passing through the window. Growing/shrinking will affect an object's mass and volume, making objects easier or harder to carry depending. Changing a human's height to be shorter and wider will affect their Vim to a more positive amount, while becoming taller allows them to reach objects farther away. However, their Vim will be lowered so they'll be unable to carry heavy objects. This can aid in situations where either strength or height is needed more than the other. The Aspect Corset can be used to manually modify one's aspect.
A similar phenomenon occurs in Homestuck as a result of Jade expanding the Fenestrated wall to enormous proportions before flying the ship through it. While she and John are crossing the Yellow Yard, they are tiny in comparison to Hussiebot. It could also be interpreted from her explanation of her spacey thing is that Witches have Aspect Modification as a class ability.