I actually, like the allen screw on the bottom mount. If you have ever had another set of two way height adjustabel coilovers, you will understand why. I have seen the lower mount on JICs, Zeals, Cuscos, and Teins all seize up to a point that they were nearly impossible to break free and adjust the height. With the allen screws used in the clamp on lower bracket, you can simply loosen the screws more and readjust if you need.
If it is still a problem for you, you could probably call Urban and order a pair of rings and use them, as well as the allen screws. Once you get the height adjusted correctly, you could also use some blue lock tight on the threads of the allens, and that should take care of your problems.