I don't know of many people running Ultralows on here, but I remember when I was researching coilovers there were quite a few discussions on the US forums.
Have you removed the adjusters on the rears? Usually with the Weitec/ST/KW kits if you spin out the adjuster half (keeping the other half in situ) then drop the front all the way you'll get low enough. You'll probs need to drop the arm off the damper to get the spring out, then the adjuster. Kinda depends just how low you want to go though. To run really slammed with any degree of practicality you need to look into camber, arch rolling etc, but I'm sure you're aware of this!
The Ultralows are 50mm down at their highest IIRC, so you're getting close to all that carry-on before you even spin them down.