The 3m number is just to illustrate that slant range is not the sole determinant of what a good missile is. I mean who would accept a modern air defense missile system that lets in most modern sea-skimming cruise missiles that routinely fly in at <10m altitudes during the terminal phase? Unless you're claiming that the land-based HQ-16 system in general is worse (or permits a higher minimum engagement altitude) than the sea-based HHQ-16 system.As for Western SAMs, there is no open source information for almost any currently operational SAM as to minimum engagement altitude, but certainly any published Russians/Chinese SAM minimum engagement altitudes (like those marketed for export) should reasonably serve as a minimum baseline for Western SAMs. The old nearly-obsolete RIM-7M Sea Sparrow already goes down to 8m. We can safely assume the newer ESSM and ESSM Block II are even lower. Tor M1 (and presumably HQ-17) goes down to 6m.
