Most CONUS LE officers need plates which will stop multiple hits of M193 and M855--neither which are threats routinely tested by NIJ. Neither steel or all compressed polyethylene plates will stop BOTH of these threats. If you are an LE officer near a current US military base, I strongly suggest getting plates which will also stop M855A1 and M80A1.
If you truly need to stop modern AP threats, why get Level IV plates which are tested against a 1940's era projectile from WWII? Would it not make more sense to test against reasonably modern threats like M993, M995, 7N37, 7N39, let alone some of the even more advanced projectiles?
Whatever threat level you get, plates must be able to stop three consecutive hits placed at each corner of a 3" triangle.
Triple curve is generally more comfortable, especially for a front plate.
SAPI sizing is generally more versatile that issuing everyone a 10x12.
Hesco and Tencate make good plates; AMI and Velocity also offer good plates.
This plate works pretty well:
https://store.atarmor.com/AT_Armor_S...at-stop-bz.htm