parameter adjusting Body not adjusting correctly

[cmullaneNH3DR]

I set the parameters of the square on the sketch and when I adjust the parameters i the box does not size correctly using the center of the square. The parameter name is "lamellafeedpipewidth" that I'm trying to change from 13 to a lower value. Please see screen cast and file.

https://autode.sk/324AyTB

[Phil.E]

The sketch rectangle you are driving with that parameter is fixed at the outer corner. Try using a coincident constraint at the middle of the rectangle to get it to change width from the middle.

The red arrows show the direction of changeUse the middle point