By mirrored version, I mean mirrored version of the 3-perm:
(L2 U2 L2 B2)2
versus:
(R2 U2 R2 B2)2
(mirrored across the yz plane)
Both do the same, but if the previous patterned ended up with R2, or even better, U2 R2, or even more... (considering the y x' move here), then the second is much...