@55mm you need to be around 4" away from the subject and while you shorten your FL then your FD will become shorter as well. That's the good thing with reversed lens, you can get the magnification you need (about 4:1 max on 18-55mm lens) which a dedicated macro lens alone (1:1) cannot provide unless you attach an ET or a diopter (some use teleconverter). But the drawback is you cannot take photos of skittish and big subject.
Most of my shots are never cropped and were taken with 18-55 kit lens...
I tried attaching a reverse len adapter to my camera (D5000) with my kit len 18-55mm. All i see is blur image through my viewfinder. I can't manual focus. I set the focal length to 55mm and I have to be very close to the subject to get the shoot. It seem to be quite tough to get those shots that you have taken Probably you would want to advise me on the tip of using a reverse len method for macro shot.