Prototype 5 is validating:
the interface between stage 1 and stage 2, at what we expected to be the final diameter of ~1.1 meter (or close to) of stage 2 for the final tower
a lever-chain system (a non domino system) to carry the destruction upward from stage 1 to base of stage 3, through the length of stage 2 (the colosseum)
again the destruction mechanisms to collapse stage 2 on stage 1, which is the final step to destroy the tower).
Here stage 3 is replaced by a thin wall as the height is limited.