Same mobs, same cons, different ass wooping.

[Brut]

Combination of RNG and the NPC level.
Generally the closer to your level the mob is, the better hit rate it'll have. Like if you're lvl9 fighting a lvl5 blue con, you're probably gonna see them miss alot of swings. But fighting a lvl7-8 blue cons they're gonna land alot more attacks for max damage.

Generally it's a good idea to fight mobs that are on the lower end of the blue con list, rather than ones that are one or two levels below you. Less resists, easier time meleeing, etc.