Controlling vertical image zoom allowing horizontal stretching

I have created my own PNG images and importing them into the "Image Full Width" block. One of these images is 1550x1000 at 150dpi (this should be fine since I read the max is 1660 with no hight restraints). Using a low DPI for web use. When I insert the PNG it cuts off the top (and bottom) and when I preview the image it zooms in where I only see a portion of the image. I have seen examples where an image fits the block and does not zoom vertically, but will allow expansion horizontally. How do you control this within Rise 360? I can't find any articles on this, just simple insert options.