However, this mechanic of lowering the Difficulty with the character's Level doesn't really happen in other Attribute Tests. Characters become more competent as they manage to increase their scores, and acquire new abilities, but jumping a 20 feet wide chasm is as difficult to do in the first level as it is in the 5th level. Characters may increase their Attributes and become more competent, or their Archetype Abilities might be able to help them more, but the Difficulty is the same.
So if you want to make combat even more challenging, simply use the Opponent's HD as the Difficulty for combat oriented Attribute Tests. This will make even lower HD creatures challenge in higher Levels, even though the players will be more competent to dispatch them. Characters with Archetypes more oriented to combate (as The Warrior or the Tough) could still subtract their Level from the HD to determine the Difficulty of their Attribute Tests, but the rest of the party could follow this new rule.
This will make combats something way riskier and will increase the value of having a combat oriented character a lot in the party. Lamentations of the Flame Princess does this with their Fighter Class and I like it a lot. The other Archetypes usually have a lot of alternative skills and abilities that make them useful in all sorts of situations and the more combat oriented classes are more limited in scope. Maybe this will help them shine brighter in the right moment and at the same time make these moments more challenging for the group as a whole.
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