For an 8:1 purchase (same as 8 sheave muscle box) you need three blocks in a cascade.
I find a cascade on the mast messy and it isn’t easy to lead the control line aft. On the mast it often interferes with the Cunningham control and/or the outhaul control specially when both have a block for dual control. IMHO a Genoa cascade sits much better on top of the CB case with the fixed ends on one side and the moving ends on the other side of the CB. The control line is easily moved aft by drilling a hole through the thwart support and adding a cleat to the slanted back side of the CB case. A flip block just aft of the cleat will allow tension control from either side of the boat, even from the hiked position.