The top 3 Tylers (Tyler, Marla, Robert) have had their defense tied to certain guns in the game.

As a made up example:

Tylers defense is tied to match the #20th best gun in the game.
Marlas defense is tied to match the #30th best gun in the game.
Roberts defense is tied to match the #40th best gun in the game.

(Not real numbers. Your mileage may vary. A littel bit of randomness has been put in on every spawn so that you can not do an apples to apples comparison against others guns).