Here is an older thread with the details of what is happening:
http://www.perceptiveautomation.com/php ... .php?t=398
It still doesn't work perfectly (as you have noticed), but given the constraints of the modules and the way the 1132CU works in offline mode, it is problematic to fix. For some modules it overshoots the dimming, but I have some that still don't dim enough. To make this more accurate, we'll have to have an internal table of all the modules that takes all of this into account. Even then it won't work well if there is much signal noise. Nasty.
The best bet is to use modules that support preset/extended dims and to use absolute dimming whenever possible. Or you can leave Indigo running. Short of that, you'll have to tweak the dim/brighten amounts to get the desired results.