A reasoning prompt can improve one deployment and degrade another.
RCCM (Reasoning-Control Capability Mismatch) examines these reversals by pairing answers to the same questions with records of how generation ends.
Across five open-weight deployments and nine strategies
Aggregate accuracy hides substantial question-level gains and harms;
a common-budget MATH500 evaluation examines transfer on a separate sample.
On 60 additional questions
concise reasoning improves Phi's automatic answer matching at a 2,048-token cap across three collections, but sharply reduces Qwen's.
Author-reviewed final-answer commitments give a smaller, statistically unresolved Phi gain.
Reserving an answer stage also improves matching, with additional input and call costs.
These results show
why a prompt benefit must be interpreted alongside its execution and evaluation:
matching a reference answer need not mean delivering it, and an apparent compression benefit may admit another explanation.
RCCM records this evidence for reproducible transfer comparisons.