IPX standards are just a marketing ploy. They give you no idea of the water resistance of a light.
Also a Kitchen sink is a poor indicator of water resistance. It needs to be under pressure or at depth for a length of time.
I am not saying the Fenix is not water resistant, just the test does not replicate real world usage.
Many years ago I put a Mag solitaire in my kitchen sink for an hour and it performed flawlessly. But when I went white water rafting it was soaked.
Almost any light with o-rings can handle sitting in a sink with water, the same goes for water resistant watches.
Watches are great examples because they use o-ring seals and have a lens.
When it comes to real world water resistance 50m (over 150 feet) is deeper than what most divers will ever do.
The way watches are rated. They are stuck into a pressure jar compressed, sitting there on the bottom. This is a hydrostatic pressure test, meaning the water does not move.
However, the second you move a watch under pressure, you increase the pressure the watch is getting on one side, while decreasing it on the other. So essentially, the second you move, you have just multiplied the pressure by many times. Now hit it on a rock while under water and imagine how much pressure there must be there!
The reality is even though less than 1% will ever actually go to 100m, let alone 200m, you need a higher rated watch for scuba because of the stresses and movement it goes through at depth.
Thats why when you see guidelines for a dive watch it looks something like this
Water Resistant: Will resist moisture from accidental splashing, rain, sweat, etc.
Water Resistant 30M: Will resist moisture and can be submerged, no swimming
Water Resistant 50M: Will resist moisture and can also be worn while swimming in shallow water.
Water Resistant 100M: Watch may be worn during snorkelling, skin-diving, and swimming.
Water Resistant 200M: (plus): Watch may be worn during standard scuba diving.
Water Resistant 1000M: Watch may be worn for deep sea diving
Think of a watch that indicates 30M of water resistance: Your pool is 10M deep so you should be safe right? Well, the force of your arm crashing down as you swim will exceed the static pressures the watch was rated for. A person will not scuba dive to depths of 200M however, if one is scuba diving then a 200M+ watch is recommended.
Hence the same reason why my maglite solitaire failed when I was white water rafting even though it performed flawlessly in the kitchen sink and pool.