The easy way to make a practice scenario "harder" is to inflate the numbers. Bump the traffic from 500 requests a second to 50,000. Add a compliance requirement. Throw in a multi-region constraint. That's what most leveled practice content actually does — same rubric, scarier inputs.
It doesn't test what leveling is actually about.
The constraints were never the hard part
A Mid-Level candidate and a Principal candidate can both correctly design a system that satisfies the exact same stated constraints — the same throughput number, the same latency budget, the same consistency requirement. If the only thing separating the tiers is whether the number in the prompt is scary, you can pass a Principal-tier bar by getting lucky on vocabulary, not by demonstrating Principal-tier judgment.
What actually separates the tiers in a real interview loop is what the interviewer expects you to volunteer, unprompted, on top of a technically correct design.
What each tier is actually graded on
Mid-Level — a working design that satisfies the stated constraints with sound fundamentals is a strong result, even if it doesn't explore every edge case. This is the bar most practice tools grade at, regardless of what difficulty label they put on the scenario.
Senior — the design has to satisfy the same constraints, but now silence about failure modes counts against you. A design that works and shows zero awareness of what breaks under partial failure gets marked down for that gap, even though nothing in it is technically broken. The bar moves from "does it work" to "do you know how it stops working."
Principal — technically satisfying the constraints stops being sufficient at all. The actual bar is organizational and cost-aware judgment: multi-region and disaster-recovery thinking, operating cost tradeoffs, blast-radius containment. A Principal-tier design that's correct but shows no sign of that higher-order reasoning scores low, on purpose — because that reasoning is the thing being tested at this level, not a bonus on top of it.
Why this has to be enforced in the grading, not just the prompt
If the rubric doesn't actually change, the tiers only differ by how intimidating the input looks. A Principal-tier submission would get graded by the exact same yardstick as a Mid-Level one — meaning the only thing separating them is whether the candidate happened to use bigger numbers correctly, not whether they demonstrated the kind of judgment a real Principal-round interviewer is actually screening for.
That's the whole reason ChaosBench's grading scales strictness by tier explicitly, not just scenario difficulty: a Senior submission with a technically sound design and zero failure-mode reasoning is graded differently than the identical design submitted at Mid-Level, and a Principal submission with no cost or blast-radius thinking is graded differently again — same design, different bar, on purpose.
If you've only ever practiced against one flat rubric, try the same kind of scenario at a higher tier and see what changes. It's usually not the numbers.