The background image provides the spatial coordinates for the table. You can load the same image for the background and overlay to get identical dimensions. 

Alternatively, you may want to reslice your template image to use the same resolution as the target image. Here is my SPM script for this purpose:

  https://github.com/rordenlab/spmScripts/...

In general, you need to be cautious about reslicing thresholded images to different resolutions, as I discuss here:

https://www.nitrc.org/plugins/mwiki/index.php/mricrogl:MainPage#Cluster_Thresholds