In Pokémon XY, how exactly does the ability "Keen Eye" work outside of battle?

Question

I am aware of the bulbapedia information regarding this, but I need more context. "From Pokémon Emerald onward, if a Pokémon with Keen Eye is in the first place in the party (even if fainted), there is a 50% chance it will prevent a random wild encounter that would have occurred if the wild Pokémon would be at least 5 levels lower than the Pokémon with Keen Eye. It shares this effect with Intimidate." Let's say, for example, I am shiny hunting. There are two Pokémon in the wild grass. One with a level chance of 2-3, and the other with a level chance of just 4 in the wild. Does this ability mean there is a 50% decrease in the 2-3 level wild Pokémon or just a decrease in the chance of the level 2 Pokémon from the Pokémon with 2-3? With a Pokémon 5 levels above the wild Pokémon. Trying to see if this ability is suitable for shiny hunting specific targets with higher levels in the wild or not.

Comments

According to Serebii, “If the Pokémon is in the lead spot, chance of encountering a low level wild Pokémon decreases by 50%. This applies to Pokémon five levels lower than *or below the level of the lead Pokémon.*”, which makes me to believe if you have a level 4 pidgey with keen eye, all the lower level encounters will be reduced by half.

---

I think keen eye would work if your first Pokemon is level 8. If it's level 7, then it would only decrease the chance of the level 2 Pokemon.