The "Validated markets" option sets the percentage of tests that must pass the validation criteria. "All" is the correct value in your case, meaning all tests must pass.

The Reactor's Multi Market feature uses the criteria set under Strategy -> Multi Market -> Validation.

You may set the Multi Market Validation criteria to correspond to the "common" Acceptance Criteria before running the Reactor.

For instance, suppose you want a strategy that performs well on both EURUSD and GBPUSD—specifically, one with a balance line stability score of 80 for both. Currently, when using multi-market analysis based on the EURUSD pair, the system might output a strategy that achieves a score of 80 on EURUSD but fails to do so on GBPUSD (seemingly because it prioritizes raw profit on the latter). This issue could likely be resolved by adding a "Use Common Acceptance Criteria for All Pairs" checkbox.