How to expand stroke width in one direction
you can't scale the stroke in AE it's fixed. But you can adjust it's stroke thickness. 



However the stroke thickness is also fixed. So if you increase the number it will be applied to all sides. So if you want to increase the TOP thickness that's not possible

In addition: By defaul AE allows you to adjust the scale on all sides but you can adjust the scale by not affecting other sides(constrain proportions)

just unclick the link icon(see image below) and adjust 


The first value allows you to adjust the length of the shape


The second value allows you to adjust the height of the shape


Adjusting the position of the anchor point has a different result. Positioning the anchor point to the end points allows you to increase or decrease that specific end point

In the picture below the anchor point is positioned at the mid bottom end point. Increasing the second value will increase the TOP HEIGHT without increasing the BOTTOM HEIGHT. Moving the anchor point on top MID end point will have an opposite effect..



Same goes for positioning the anchor point on the side