The placement of expressions is controlled in the category designer. Go to the expression box, pick "Tempo Marks," then click the "Edit Categories" button below the list of expression categories. That will open the dialogue where placement, font, etc. of the expressions in that category go. As you can see, tempo marks are set to be placed "Start of Time Signature"--which is the correct place for them. If you want to place a tempo expression anywhere else, you will have to change that to one of the more than a dozen options. But, remember that whatever you change here will apply to all expressions in that category.
