Bob, I would not get to hung up on if you are shooting at 1.5:1 or 1:1. Just know that when compared to a full frame camera even though you are technically shooting at 1:1 your image would appear to be shot at 1.5:1. But really that makes little difference, most macro shooters are going to crop their images anyway so that they can display their subject as large as they can while preserving image quality... so in the end the question you are posing is not really very significant. The lens that you are asking about is going to preform as well as any macro lens out there so the question is purely academic as unless you change over to something like Canon and purchase a MP-E 65 that goes up to 5:1 mag, but as it is 1:1 is all the magnification that your going to get out of a conventional lens on your camera.

There are other things that you can do to increase magnification beyond the 1:1 ratio such as by adding extension tubes, or purchasing filters which will magnify your image... or in my case I use wide angle lenses mounted backwards to my camera.... But as far as aspect ratio it is really something that you should not get to hung up on... too many people think far too hard about the difference between aspect ratios on a full frame and a crop sensor camera. What is important is understanding the camera that you have.