Sometimes, when using origin planes to position a part, you know that your final constraint will need to be either a mate or a flush. It is important to observe the selection vector previews to determine if you want your arrows pointing towards each other (mate) or pointing in the same direction (flush).
In the browser, select the XZ plane in the origin folder for the assembly. Then, select the XZ plane in the origin folder for the cover.
Tip: When the expected preview of the constraint does not happen try reversing the constraint solution.
Click Flush in the Solution field of the Place Constraint dialog box. The constraint now previews (click the following illustration to see the preview).
Click OK to create the constraint and close the dialog box. The cover is fully positioned.