I am unsure how you are measuring tiller however, on traditional style single cam bows, it is better to tie a string between both axles and then measure from the tied-in string to the limb base rather than measure from the bowstring to the limb base. The reason is that the idler wheel and single cam are usually of different diameters and thus the bowstring is at a slight angle. This can/does throw off tiller measurements.

I would bottom out both limbs and then back them off equal turns and measure using the method I described above.