To more accurately estimate the true/effective size of the dots, we assume that they are at least 2 nm smaller than measured by SEM, giving an effective dot radius of ~6 nm. Therefore, all dots with a 𝑅 " > 17 are defined as a fluctuational (or point) defect. The physical interpretation of this defect definition is clear: if the read/write head is moved to the expected location of a nearest neighbour (based on perfect hexagonal lattice) and the registration error is greater than 17%, the dot will not be detected.