Tick, how are you adding spacers to raise the ride height?? also you shouldn't use shock mounting positions to raise or lower the car.
What length are you building your shocks at? Mine are all 67mm from the lowest point on the ball cup to the highest point in the upper pivot hole.
If you can't get the lower ride height with the shumacher springs then you may want to switch to Associated springs which are shorter, or very carefully use a dremel and cut the shuie springs(making sure they are the same length after cutting).
Personnally I run my Mission at 5.5-6mm and feel there are no ill effects, and don't even need to go lower.