I underestimated the minimum amount of fiberglass-reinforced, self-levelling screed necessary to fill the irregularities in the concrete crown. I used 50 kg of screed, which produces about 24 liters of product. This was far too little, - half as much as I should have used. In order for screed to flow to a level surface around the ring, the fluid mass must be at least 2 cm deep, preferably 3 cm. I will try again, this time using 100 kg of screed (48 liters). Most of the bolts are long enough to allow for this extra thickness. In those few places where the bolts are not be long enough, I will drill new holes for expansion bolts.