For n=13, I applied random similarity transforms (rotation, scale, translation) to the published configuration, rounded every coordinate to the nine-decimal unit-square grid, and scored each grid image by exact integer pairwise squared distances. A transform with ratio 3.1511959331143129... rounds upward to 3.151195934, improving 3.151195936. The same transform search can be run for other P52 rows; all comparisons use exact max/min squared distances before the final upward rounding.
P52 · Smallest ratio of largest to smallest distance · Discussion