Simplestore image preview window default dimensions don't fit image

Since upgrading to Sitebuilder Plus, the default dimensions of the Simplestore image preview window are width=420, height=620 (these appear hardwired in the HTML).  These dimensions are inappropriate for my product images which are all landscape.  It is possible to resize the window to see the image at a reasonable size but my customers shouldn't have to do that.  Is there a way to get the window to fit the image by default?