Skyflash min alt is from its proxy fuse triggering on the ground not MP.
Sea Harrier FA2 had a specific design requirement to track and engage sea-skimming anti-ship missiles. which it could do. (notably weapon systems like EXOCET which have a flight height of around 10-15m)
MP hasnt really been a “thing” (affecting missiles) since the 1980s
yeah water massively reduces blasts not entirely but a lot (irl and in game) its also why in ground rb if your bomb lands in water it can sometimes not work as well
Multipathing alone will not save you from high altitude launched fox 3’s. Another reason why having control of altitude is very important in the meta, and we all know whose planes are and aren’t allowed to climb right now.