The initial heuristic proposal suggests that for a new transaction to replace an existing one, it must not only have a higher mining score but also contribute a higher total fee than the sum of all transactions it displaces. This approach involves evaluating the mining scores of new transactions against those of conflicting transactions cached in the mempool.

An alternative strategy focuses on the overall improvement of the mempool through replacements. It emphasizes creating a mempool post-replacement that is objectively better than the current one. This is assessed by comparing fee vs. size diagrams before and after replacements, ensuring that the new mempool configuration provides a clear advantage over the previous state. The process entails identifying affected clusters by a replacement, calculating their fee vs. size diagrams, simulating the removal of conflicts and addition of the new transaction, and re-evaluating the clusters' diagrams to confirm an enhanced mempool state.

Despite these methodologies, challenges arise in guaranteeing the mempool's qualitative improvement solely based on the heuristic approach. An illustrative example demonstrates a scenario where a replacement transaction passes the heuristic test but fails to make the mempool strictly better, as indicated by the comparison of fee vs. size diagrams before and after the transaction replacement. This discrepancy raises concerns about the effectiveness of the heuristic method in ensuring mempool optimization.

Given these observations, several questions emerge regarding the viability of the heuristic approach, the potential need for additional rules to ensure mempool enhancement, and whether the fee-size diagram metric should be the primary validation tool for RBF operations. The considerations include the technical complexities of implementing such a system and its ability to accurately reflect the desired improvements in the mempool's state, alongside assessing its vulnerability to transaction pinning scenarios.