According to the UUC web site, the rears have a middle position as well. Use an outside hole on one side and an inside hole on the other for a "middle" stiffness.
I have mine set up - middle front and middle rear, which seems to be the best balance.
Stiff, stiff is ok if that's the way you like it. I don't like to rely on sway bars for negating body roll, use springs shocks instead and use sways for tuning. Sways that are too stiff are not a good thing either, though the UUCs are not the thickest out there.
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