5.11 lists the following fit information for plates: "Fits 24mm wide medium (12.5" H x 9.5" L x 2" W) and large (13.25" x 10.25" x 2.25") SAPI plates"
Since the only other answer here was completely useless. I did some digging and found that a 10x12 "will" fit in this. However a 11x14 will "not" fit. 11x14 is considered an extra-large SAPI plate, and this carrier only supports upto large sapi plates. (Which is the size between the large and extra-large.)